To evaluate the risk factors for serous, mucinous and endometrioid ovarian cysts, data were collected in a case-control study conducted in the greater Milan area based on 202 women with benign cysts (114 endometrioid and 88 serous or mucinous) of the ovary and 1127 controls. Questions were asked about menstrual and reproductive characteristics, marital status, education, history of various diseases, and lifetime use of oral contraceptives and other hormonal treatments. Higher social class, earlier menarche and longer interval between age at first marriage and first birth, a likely indicator of subfertility, were associated with an increased risk of serous, mucinous and endometrioid cysts. Women with endometrioid cyst were characterized by low parity, less frequent irregular or long menses, more frequent oral contraceptive use and low body mass index, while the most relevant risk factor associated with serous and mucinous cysts was greater age at first birth. The present data point out the epidemiological differences between endometrioid and serous or mucinous cysts. Further, they suggest that analyses of risk factors for epithelial ovarian cancer subdivided by various histotypes may be of interest in order to confirm possible heterogeneities in the aetiology of ovarian epithelial neoplasms.