Misdiagnosis and Delayed Diagnosis Claims in Arizona

By Joe Styler, editor (not an attorney). Updated October 9, 2026. Sources checked

A missed, wrong or late diagnosis can shape everything that follows. Under Arizona law, though, a diagnostic error is not automatically medical malpractice. A claim has to prove two elements set out in a statute, and Arizona has its own rules about expert opinions and deadlines. This page explains them in plain terms. It cannot tell you whether your situation meets them.

What Arizona law asks in a diagnosis case

Arizona’s malpractice chapter defines a medical malpractice action as a claim for injury or death against a licensed health care provider. The claim must be based on alleged negligence, misconduct, errors or omissions, or breach of contract in providing health care, or on care given without express or implied consent (A.R.S. 12-561). A malpractice action against a licensed provider may be brought only on those grounds (A.R.S. 12-562).

The proof comes from A.R.S. 12-563. It says both of these are necessary elements:

1. The provider failed to use the care, skill and learning expected of a reasonable, prudent provider in the same profession or class in Arizona, acting in the same or similar circumstances.
2. That failure was a proximate cause of the injury.

A missed or late diagnosis can be part of the facts behind either element. It does not prove either one by itself. The statute looks at the care that was given, and at whether that care caused the harm, rather than only at whether the diagnosis turned out to be right.

The first element: the care that was given

The first element compares what the provider did with what a reasonable, prudent provider would have done. In a diagnosis case, the words “the same or similar circumstances” do a lot of work. They point to the situation the provider was in at the time. A diagnosis that looks plain months later, after an illness has developed, may not have been plain at the first visit. The comparison is with a reasonable provider facing the circumstances of that visit.

When people think a diagnosis was missed, the facts they and their lawyers often look at include:

• what symptoms and history the patient reported, and whether they were written down
• which tests were ordered, and whether the findings were followed up
• whether the patient was referred on or told when to come back

Whether the answers show a failure to meet the standard is something a qualified expert and a lawyer would have to assess.

The second element: did the delay change the outcome?

The second element is proximate cause: the provider’s failure has to be a proximate cause of the injury. In a diagnosis case, this is often the hard part. In plain terms, the question is generally whether an earlier or correct diagnosis would have changed what happened to the patient.

Some conditions may have been easier to treat if found sooner. Others may have followed the same course either way. Because 12-563 requires both elements, showing that a provider fell short is not enough if the shortfall did not cause the injury. That is a medical question as much as a legal one.

Expert support: the certification and the affidavit

Arizona has an early expert step for claims against a health care professional. Under A.R.S. 12-2603, the person bringing the claim must certify, in a written statement filed and served with the claim, whether expert opinion testimony is needed to prove the standard of care or liability. If it is, a preliminary expert opinion affidavit must be served with the initial disclosures. The affidavit must state, at least, the expert’s qualifications, the factual basis for each claim, the acts, errors or omissions the expert considers a violation of the standard of care, and the way they caused or contributed to the damages.

Those last two items line up with the two elements in 12-563. In a diagnosis case, the affidavit is often the first place a qualified person has to say what should have been done and how the miss led to harm.

If a required affidavit is not filed and served, the court shall dismiss the claim against that professional without prejudice. The statute gives a reasonable time to cure an affidavit only when it is challenged as insufficient, if needed. That is not a grace period for never serving one.

A.R.S. 12-2604 limits who can give standard-of-care testimony. Among other things, the expert must be licensed as a health professional, must match the defendant’s specialty if the defendant is or claims to be a specialist, and may not be paid a fee that depends on the outcome. Our page on the expert affidavit requirement explains these rules in more detail.

When the two-year clock starts in a diagnosis case

A.R.S. 12-542 generally requires a medical malpractice lawsuit to be started within two years after the cause of action accrues. That is not necessarily two years from the visit where the diagnosis was missed.

In Walk v. Ring (2002), the Arizona Supreme Court said a medical malpractice claim accrues when a reasonable person would be on notice to investigate whether the injury came from someone’s wrongdoing. A bad result alone is not always enough to start the clock, and when a claim accrued is generally a question for the jury. This is not a promise of a later start date. The date can be disputed, so assume it could be earlier than you hope.

Other rules can change the timing:

• If the patient died, 12-542 counts the two years from the date of death.
• Claims involving a public entity, public school or public employee need a notice of claim within 180 days after the cause of action accrues (A.R.S. 12-821.01). A lawsuit against a public entity or public employee must be brought within one year after accrual (A.R.S. 12-821). Our page on claims against public hospitals in Arizona covers these steps.
• Arizona has a tolling statute, A.R.S. 12-502, for minors and people of unsound mind, for the claims it covers. Check any child’s deadline with a lawyer.
• Care at a federal facility follows different rules not covered here, so ask a lawyer soon.

Our page on the Arizona medical malpractice statute of limitations sets these clocks out side by side. Sending our form does not stop or pause any deadline.

Not sure when you first had reason to question a diagnosis? Request a free case review.

Missed diagnoses in the emergency room

Arizona sets a higher standard of proof for some emergency care. Under A.R.S. 12-572, for a patient of a licensed hospital in compliance with the federal emergency treatment law, or as a result of a disaster, the two elements in 12-563 must be proved by clear and convincing evidence. The statute applies the same rule to the hospital and its agents and employees in those cases.

That rule does not cover all ER care, and it does not bar ER claims. Whether a visit falls within it is a question for a lawyer. Our page on emergency room malpractice in Arizona explains the rule and the federal law behind it.

If a provider apologized

A.R.S. 12-2605 says that in a civil case against a health care provider, a statement, gesture or conduct expressing apology, sympathy or responsibility about an unanticipated outcome of medical care is inadmissible as evidence of an admission of liability or as evidence of an admission against interest.

In plain terms, an apology is not proof of malpractice in court, and it does not rule it out either.

What to gather now

You do not have to decide whether the care met the standard. You can put the facts in order:

• the dates of each visit, call, test and referral connected to the problem
• the symptoms you reported at each visit, as well as you remember them
• which tests were ordered, when the findings came back, and whether anyone told you about them
• when the correct diagnosis was made
• when you first had reason to think the earlier diagnosis was wrong, and how you learned it
• whether any of the care was at a public or federal facility, if you know

Your medical records will show much of this. Our page on how to get your medical records in Arizona explains how to ask for them. See also Arizona medical malpractice law explained and how a claim works in Arizona.

Frequently asked questions

Is a misdiagnosis automatically medical malpractice in Arizona?

No. Under A.R.S. 12-563, a claim must prove two things: that the provider failed to use the care, skill and learning expected of a reasonable, prudent provider in the same profession or class in Arizona in the same or similar circumstances, and that this failure was a proximate cause of the injury. A wrong or late diagnosis may be part of the facts, but it does not prove either element by itself.

Do I need a medical expert for a misdiagnosis claim?

Under A.R.S. 12-2603, the person bringing the claim must certify whether expert testimony is needed to prove the standard of care or liability. If it is, a preliminary expert opinion affidavit must be served with the initial disclosures, and if a required affidavit is not filed and served, the court shall dismiss the claim without prejudice.

Does the deadline start on the day the diagnosis was missed?

Not necessarily. A.R.S. 12-542 generally allows two years after the cause of action accrues. In Walk v. Ring (2002), the Arizona Supreme Court said a malpractice claim accrues when a reasonable person would be on notice to investigate whether the injury came from someone’s wrongdoing, and that a bad result alone is not always enough. Claims against public bodies have much shorter deadlines. Sending our form does not stop or pause any deadline.

The provider apologized. Does that prove malpractice?

No. A.R.S. 12-2605 says a statement expressing apology, sympathy or responsibility about an unanticipated outcome of medical care is inadmissible as evidence of an admission of liability in a civil case against a health care provider. The two elements of a claim still have to be proved in other ways.

Is a missed diagnosis in the ER treated differently?

Sometimes. A.R.S. 12-572 requires clear and convincing evidence of both elements for care of a licensed hospital’s patient given in compliance with the federal emergency treatment law, or as a result of a disaster. It does not apply to all ER care and does not bar ER claims. Whether it applies to a particular visit is a question for a lawyer.