The relation between the use of combination oral contraceptives (OCs) and the risk of epithelial ovarian cancer was investigated in a case-control study conducted in Milan on 209 women below the age of 60 with histologically confirmed epithelial ovarian cancer, and 418 age-matched controls with a spectrum of acute conditions apparently unrelated to OC use. Combination oral contraceptives were used by 18 (9%) cases, and 59 (14%) controls, giving a relative risk estimate of 0.6 (95% confidence interval = 0.3-1.0, P less than 0.05). The risk of ovarian cancer decreased with increasing duration of use and the point estimate remained below unity long after cessation of use. These results were not accounted for by parity, infertility, or other identified potential confounding factors. Thus, the findings of the present study add further support to the evidence emerging from American data of a reduction of approximately 40% in the risk of epithelial ovarian cancer among women who had used oral contraceptives.