It is likely 2 years from the date of injury/harm/malpractice. See, http://www.azleg.state.az.us/FormatDocument.asp?inDoc=/ars/12/00542.htm&Title=12&DocType=ARS
However, often many factors, such as specific facts surrounding the potential case, may alter the statute of limitations, so it may be in your best interest to seek legal assistance with determining the statute of limitations and/or in general with your potential medical malpractice case. Best of luck!
NOTE: This response is general in nature and should not be considered legal advice. No attorney-client privilege exists or is formed by this response.