Between November 1981 and March 1983, data were collected to evaluate risk factors for benign breast lesions in a case-control study based on 288 women with histologically proven benign breast disease, admitted for biopsy to the Tumor Institute of Milan, and 285 age-matched 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. Nulliparity or low parity, late age at first birth, and late menopause were associated with an increased risk of benign breast disease. The elevated risk associated with late age at first birth was not accounted for by parity. Early age at menarche was associated with an increased risk, but the estimate was not statistically significant. The data do not suggest that the use of oral contraceptives or other female hormones (such as estrogen replacement therapy) is related to the risk of benign breast disease. Risk was apparently lower, however, among current and long-term oral contraceptive users. There was no evidence of a trend with reference to body mass index. The present data indicate a substantial agreement between the risk factors for (pathologically confirmed) benign and malignant breast disease, not only directly, by showing a relationship with parity, age at first birth, and age at menopause, but also indirectly, by failing to produce evidence that greater weight or the use of oral contraceptives has a protective effect.