The relationships between reproductive factors, exogenous hormones and renal-cell cancer were examined in an international, multicenter, population-based, case-control study undertaken in 1989-1991. Data from 5 centers situated in Australia, Denmark, Germany, Sweden and the United States included for analysis 608 women with renal-cell cancer and 766 female controls. A significant trend in risk (p = 0.002) was associated with number of births, with an 80% excess risk for 6 or more births [RR = 1.8, 95% confidence interval (CI) = 1.1 to 2.9] compared with one birth. A decreasing risk was seen for increasing age at first birth, although this was confounded by body-mass index and number of births. A suggestive reduction of risk was also seen for increasing age at menarche. Age at menopause was unrelated to risk of renal-cell cancer. An increased risk was observed for women having had both a hysterectomy and an oophorectomy. Use of oral contraceptives in non-smoking women reduced the risk of renal-cell cancer (RR = 0.5, 95% CI = 0.4 to 0.8); this reduction increased with longer duration of use. No association was observed for estrogen replacement therapy. Our results indicate that certain hormonal and reproductive variables may be related to risk of renal-cell cancer and deserve further investigation, both epidemiologically and experimentally.