In recent years cases have been brought in various jurisdictions involving claims against doctors by persons who are not their patients. The claims have related to AIDS and other sexually communicable diseases which the persons in question have contracted from the doctors' patients. In these cases, the courts have held that doctors owe a duty of care in negligence to warn the sexual partners of their patients (usually via the patients) of the risks involved in participating in a sexual relationship with these patients. This article examines and analyses the relevant cases and considers the direction which the law in this area is likely to take both in Singapore and other Commonwealth countries.