A population-based case-control study of risk factors for renal-cell carcinoma was conducted in Denmark from 1989 to 1992. A total of 368 histologically verified cases and 396 controls were included. Information on weight, height, physical activity and reproductive factors were collected in a structured interview, along with information on other suspected risk factors. A significant increase in risk was seen for obese women but not obese men. Although there was no clear gradient, the risk was highest among women with a relative weight in the upper 5% (OR 6.1; 95% CI, 2.3 to 16.1). The increased risk was most evident for high relative weight in ages 30 to 50. No association was observed for height or physical activity. Use of amphetamines was associated with increased risk but, because of the close link with obesity, we were unable to provide evidence that amphetamines are an independent risk factor. We found some evidence for an association with reproductive variables, including decreased risk for women with late menarche and first pregnancy and birth. We observed no association with number of pregnancies or age at menopause, or use of estrogen-containing medication.