Throughout history, doctor-patient confidentiality has been a cornerstone of Western medical practice. The duty to keep patients’ information private is written into the codes of ethics of medical organizations, and is even in the Hippocratic oath: “What I may see or hear in the course of treatment,” it says, “I will keep to myself.”

Patients allow physicians into their private lives on the condition that the information we learn will not be used against them. I once took care of a business executive in the emergency room who had hired call girls during a weekend drug binge. When he saw a police officer outside his room, he quietly handed me an envelope containing a large amount of white powder. I wasn’t sure what to do with it, so I discarded it. For the next several hours the patient eyed me suspiciously, probably wondering whether I had ratted him out. But it never occurred to me to do so.

Of course, like all ethical imperatives, doctor-patient confidentiality is not absolute. Doctors have to disclose private information when it is clearly in the patient’s interest (documenting a drug allergy in the medical record, for example) or when it comes to complying with a court order (as in cases of child abuse). We must also betray confidentiality when it is in the “public interest” (reporting infectious diseases, for example).

The duty to warn third parties in danger is also an important exception to confidentiality. We publicly disclose the identities of sex offenders. We alert family members when hereditary diseases in our patients come to light. A colleague of mine once took care of a patient, a school bus driver, who received an implantable defibrillator after suffering cardiac arrhythmias. When my colleague advised the man to quit his job because of the potential risk to young children, the man refused, so my colleague reported him to the Department of Motor Vehicles. It was an action that my colleague felt very comfortable taking, even though it created an irreparable rift in that relationship.