This report reviews the medicinal agents that have been linked to human cancer, with emphasis on recent evidence implicating estrogenic compounds such as DES, menopausal estrogens, and oral contraceptives. Attention is also given to drugs that have fallen under suspicion and requires further epidemiologic evaluation. The detection of drug-cancer associations not only influences clinical and public health practice, but may also provide insights into mechanisms of carcinogenesis. The clinician contributes to the prevention of drug-induced cancer by being alert to iatrogenic hazards and cooperating in epidemiologic investigations, by weighing risks versus benefits in individual cases, and by discussing with patients the rationale and risks of proposed forms of therapy.