The Expert Affidavit in an Arizona Medical Malpractice Case

By Joe Styler, editor (not an attorney). Updated October 8, 2026. Sources checked

If you have talked to a lawyer about a possible medical malpractice claim in Arizona, you may have heard that the lawyer needs “an expert”. That idea comes from two Arizona statutes. A written statement about expert testimony is filed with the claim, and, if expert testimony is needed, the expert’s sworn opinion follows early in the case. A.R.S. 12-2603 says when that opinion has to be served and what it must contain. A.R.S. 12-2604 sets the qualifications for anyone who gives expert testimony on the standard of care. This page cannot tell you whether your own situation needs an expert or whether you have a claim. A lawyer can look at your facts and answer that.

This page is part of our guide to how a medical malpractice claim works in Arizona.

Step 1: A written statement about whether an expert is needed

Under A.R.S. 12-2603(A), the person bringing a claim against a health care professional (or their attorney) must file and serve, with the claim, a written statement saying whether expert testimony is needed to prove the professional’s standard of care or liability.

A party who names someone outside the case (a nonparty) as being at fault has the same duty for that nonparty.

Step 2: The preliminary expert opinion affidavit

If the statement says expert testimony is needed, a second document follows: a preliminary expert opinion affidavit. An affidavit is a written statement made under oath. A.R.S. 12-2603(B) says it must cover four things:

1. The expert’s qualifications to give an opinion on the standard of care or liability.
2. The factual basis for each claim against the health care professional.
3. The acts, errors or omissions that the expert believes broke the applicable standard of care.
4. How those acts, errors or omissions caused or contributed to the damages or other relief sought.

More than one expert may be used.

Why those four items matter

Items 3 and 4 match what a claim has to prove under A.R.S. 12-563. First, the provider failed to use the degree of care, skill and learning expected of a reasonable, prudent provider in the same profession or class in Arizona, in the same or similar circumstances. Second, that failure was a proximate cause of the injury. The affidavit is where an expert first puts in writing an opinion on both questions.

Step 3: When the affidavit is due

A.R.S. 12-2603(B) ties the timing to the start of the case:

• For the person bringing the claim: the affidavit is served with the initial disclosures required by Rule 26.1 of the Arizona Rules of Civil Procedure. Initial disclosures are the first information each side must share in a lawsuit.
• For a party that names a nonparty at fault: the affidavit is due within 60 days after that party files its designation.
• Extensions: under 12-2603(C), the court may extend the deadline for good cause, or the parties may agree to an extension by stipulation.

These deadlines run inside a case already filed. They are separate from the deadline for filing the case, covered on our page about the Arizona medical malpractice statute of limitations. Sending our form does not stop or pause any deadline.

Step 4: When the two sides disagree about needing an expert

If the person bringing the claim certifies that no expert is needed and the other side disagrees, A.R.S. 12-2603(D) and (E) apply:

• If the certification is disputed in good faith, a party may ask the court to order a preliminary expert opinion affidavit, and the court decides.
• While that request is pending, other proceedings and time periods concerning that claim are put on hold (the statute calls this a stay) until the court rules.

Step 5: What happens if a required affidavit is missing

Under A.R.S. 12-2603(F), the court must dismiss the claim against the health care professional without prejudice if a required affidavit is not filed and served. “Required” here means either the claimant certified that expert testimony is needed, or the court ordered an affidavit.

“Without prejudice” means the dismissal is not a ruling on whether the claim is right or wrong. Whether a dismissed claim could be brought again depends on the dates and other rules. That is a question for a lawyer.

If an affidavit was served but is challenged as insufficient, the court must give a reasonable time to cure the problem, if needed. That time to cure applies to an insufficient affidavit, not to a missing one.

Under 12-2603(G), the person bringing the claim may later add claims, evidence or expert opinions, as long as they are disclosed on time or the court allows them.

Step 6: Who counts as a qualified expert

A.R.S. 12-2604 sets the rules for anyone who gives expert testimony on the standard of care in an Arizona medical malpractice case.

Rules for every standard of care expert

• Licensed. The expert must be a licensed health professional, in Arizona or in another state (12-2604(A)).
• Recent practice or teaching. In the year before the events in the case, the expert must have spent the majority (more than half) of their professional time in active clinical practice in the same health profession, and specialty where one applies, or teaching in an accredited program in it (12-2604(A)(2)).
• No fee that depends on the outcome. An expert may not testify if their fee depends on how the case comes out (12-2604(D)).
• The court still decides. These rules do not stop a court from disqualifying an expert on other grounds (12-2604(C)).

Matching the expert to the defendant

This table summarizes 12-2604(A) and (B):

If the defendant is	The standard of care expert must
A specialist, or claims to be one	Have specialized in the same specialty (or claimed specialty) at the time of the events in the case
A board-certified specialist	Have specialized in the same specialty and be board certified in it
A general practitioner	Have spent the majority of professional time in the year before the events in active practice as a general practitioner, or teaching in the same health profession in an accredited program
A health care institution that employs the health professional involved	Meet the same rules that would apply if that health professional were the defendant

A note on emergency care

For care of a licensed hospital’s patient given in compliance with the federal emergency treatment law or as a result of a disaster, A.R.S. 12-572 requires the elements of the claim to be proved by clear and convincing evidence, a higher standard; our page on emergency room malpractice in Arizona explains it.

Have questions about your dates and facts? Request a free case review.

How the medical records exchange fits in

Rule 26.3 of the Arizona Rules of Civil Procedure is a separate disclosure rule for medical malpractice cases. In general terms:

• Medical records are exchanged early. The person bringing the claim gives their available relevant medical records to the defendant. Each defendant then gives the plaintiff and the other parties copies of the plaintiff’s available relevant medical records.
• It says the sides’ experts on the standard of care and on causation are disclosed at the same time, unless the parties agree otherwise or the court orders otherwise for good cause.

Rule 26.3 does not set a date for expert disclosure. The rule also sets day counts for the records exchange, but we have read it only in unofficial copies, so this page leaves those numbers out.

Why lawyers usually get records and an expert review before filing

Put together, the affidavit is due early in the case, it must state the facts, the breach and how it caused the harm, and a missing required affidavit means dismissal. An expert who testifies on the standard of care must also meet the 12-2604 rules for that particular defendant. That is why, in practice, a lawyer looking at a possible medical malpractice claim usually starts by gathering the medical records and having them reviewed by a qualified expert before deciding whether a case can be brought.

What this means for you

• Gather what you have. Bills, discharge papers, appointment dates and any records you already hold help a lawyer get started.
• Write down dates. When the care happened and when you first suspected a problem are both useful to a lawyer.
• Do not wait on the expert question. The general filing deadline in A.R.S. 12-542 is two years after the claim accrues, and claims against public bodies have shorter ones (see our page on claims against public hospitals in Arizona). Working out when the clock started can be complicated, and different timing rules can apply to children. A lawyer can look at your dates and facts. Sending our form does not stop or pause any deadline.

Frequently asked questions

Does every Arizona medical malpractice claim need an expert affidavit?

No. A.R.S. 12-2603 requires the person bringing a claim against a health care professional to state in writing whether expert testimony is needed. An affidavit is required when that statement says expert testimony is needed, or when the court orders one after the other side disputes the statement. The Arizona Supreme Court has said expert testimony is normally required, and is not needed only when the lack of care is something ordinary people could recognize and judge without help (Francisco v. Affiliated Urologists, 2024). A lawyer can say whether that could apply to a particular case.

What happens if the affidavit is not served?

If a required affidavit is not filed and served, the court must dismiss the claim against the health care professional without prejudice. If an affidavit was served but is challenged as insufficient, the court must give a reasonable time to cure it, if needed.

Can the expert be from another state?

Yes. A.R.S. 12-2604 says the expert must be a licensed health professional in Arizona or another state, and must also meet the specialty and recent practice or teaching rules that fit the defendant.

Can an expert be paid only if the case wins?

No. Under A.R.S. 12-2604, an expert may not testify if their fee depends on the outcome of the case.