Arizona’s One Expert Per Issue Rule in Medical Malpractice Cases

In order to win a medical malpractice case in Arizona, the person bringing the claim (the plaintiff) must prove that the defendant medical care provider’s actions fell below the applicable standard of care and that the defendant’s actions caused the plaintiff’s injuries.  In most cases, expert witness testimony is necessary to prove the elements of the plaintiff’s case.  The number and type of experts that can be used in a medical malpractice case are strictly controlled by Arizona law.  This blog post will briefly discuss one of these controls: Arizona’s one expert per issue rule.

Arizona Rules of Civil Procedure Define the One Expert Per Issue Rule

Court rules that govern medical malpractice claims provide that each side of a case “is presumptively entitled to call only one…expert to testify on an issue.”  Ariz.R.Civ.Pro. 26(b)(4)(D).  In practice, this means that the plaintiff and defendant are usually limited to one non-party expert on the issue of standard of care and one expert on the issue of causation.  The rule is designed to limit the temptation for one side of a case to present a parade of experts designed to overwhelm the jury with sheer volume.  However, the rule has also been used by lawyers who represent medical care providers to attempt to limit the presentation of necessary and relevant expert testimony by the plaintiff.

Hardt v. AZHH, LLC, Ca-CV 15-0532 (Ariz. App. 2017).

One such example of a defendant using the One Expert Rule to try to limit relevant expert testimony by the plaintiff is found in a recent Arizona Court of Appeals decision Hardt v. AZHH, LLC.  In Hardt, the trial court granted the defendant’s motion to prevent the plaintiff’s vascular surgeon expert from testifying in the trial.  This helped lead to a verdict in favor of the defendant.  However, the plaintiff appealed the trial court’s decision to the Arizona Court of Appeals which reversed the trail court’s ruling because, it said, the rule was intended to limit only “cumulative evidence,” i.e. evidence that tends to establish a point already proven by other evidence, not to exclude relevant, necessary evidence that the jury should have been able to consider.  In other words, if the testimony of an expert does not repeat what was presented by other experts, it is not “cumulative” and the plaintiff should be allowed to present the testimony of both experts to the jury.  The Hardt case may be subject to review by the Arizona Supreme Court.

Know Your Rights Regarding Medical Malpractice Claims

Medical malpractice cases are complex and require specific and unique expertise.  If you or someone you know has been injured as a result of a medical mistake, it is important that you contact an attorney that has the knowledge and experience to explain your rights and who understands the unique rules involved in medical malpractice claims.  If you have questions, call attorney Brian Allen at (480) 461-5335 or contact him at for a free consultation to discuss your rights and options.


This blog should be used for informational purposes only. It does not create an attorney-client relationship with any reader and should not be construed as legal advice. If you need legal advice regarding One Expert Per Issue Rule, or any other personal injury, please feel free to contact Brian T. Allen at  480.461.5335,  log on to,  or contact an attorney in your area. Udall Shumway PLC is located in Mesa, Arizona and is a full service law firm. We assist Individuals, families, businesses, schools and municipalities in Mesa and the Phoenix/East Valley.