Epidemiologic and laboratory data suggest an effect of oral contraceptives (OC) on the risk of malignant melanoma. This relationship was explored in a hospital-based case-control study of 160 women with malignant melanoma and 640 matched controls, all of whom were white and 20-59 years of age. A total of 63 cases (39%) had used OC compared with 270 controls (42%), yielding a relative risk estimate of 0.9 (95% confidence interval: 0.6-1.3). When a number of potential confounding factors were simultaneously controlled, the relative risk estimate was 0.8 (0.5-1.3). For use that lasted 5 or more years the estimate was 0.9 (0.5-1.6). The level of tumor invasion was not related to OC use. The evidence from this study suggests that OC, even when used for 5 or more years, do not increase the risk of malignant melanoma.