A "statute of limitations" is a law that sets a limit on the amount of time you have to file a civil lawsuit after you've suffered some type of harm or loss. Arizona's statute of limitations for medical malpractice lawsuits can be found at Arizona Revised Statutes section 12-542(1). It states that a legal action alleging malpractice by a health care professional or care facility must be filed within two years "after the cause of action accrues."
Under what's known as the "discovery rule," Arizona courts have held that "the cause of action accrues" in a medical malpractice case when the plaintiff (the patient who's suing) knows, or should reasonably know, that a negligent medical error caused the patient's injuries or losses.
Keep in mind that when you are relying on the discovery rule, it will be up to you to prove that you did not learn that you had a medical malpractice claim—and could not have discovered that if you had exercised reasonable diligence—until less than two years before you filed your lawsuit. That may be difficult to prove if, for example, you experienced unexpected medical problems after treatment that should have alerted you to the possibility of your doctor's negligence, but you didn't investigate or take action for more than two years.
There are limited circumstances that will extend the two-year deadline for filing a medical malpractice suit. For instance, the "clock" is paused (or "tolled" in legal jargon) while the plaintiff is under the age of 18 or is mentally disabled.
Unless one of these exceptions applies, if you file your lawsuit more than two years after the medical error happened, the health care provider that you're trying to sue will likely file a motion asking the court to dismiss the case. And if the judge finds that you waited too long, your case will almost certainly be dismissed.
So it's critical that you pay attention to the two-year statute of limitations and speak to a lawyer as soon as you have reason to believe that you may have suffered harm because of medical malpractice. (Learn more about the basic requirements for a medical malpractice claim.)