Physician organizations have long supported full disclosure of serious medical errors to patients. The authors analyze various ethical arguments for and against disclosure, outlining the potential risks and benefits to patients and physicians. The article also describes the ethical duty of physicians to disclose errors, which is derived from the fiduciary nature of the doctor-patient relationship, and strongly advocates for full disclosure except in rare instances. Finally, practical issues in the disclosure of mistakes are outlined, including the challenges of when, who, what to say, and what to do regarding errors made by other physicians.