Individuals whose energy intake exceeds expenditure are at increased risk of colorectal cancer. To determine whether body-size measurements at different ages were risk factors for cancer of the colon-rectum, we carried out a hospital-based case-control study in 6 Italian areas, 2 of which were in the South. Interviews were conducted with 1,217 subjects of both genders with incident histologically confirmed cancer of the colon, 726 with cancer of the rectum, and 4,136 controls hospitalized for acute, non-neoplastic, non-digestive conditions. The questionnaire included information on sociodemographic factors, and physical activity, a validated dietary history, height, weight at diagnosis and at 12, 30 and 50 years of age and waist-to-hip ratio (WHR). After allowance for education, physical activity, energy intake, family history of colorectal cancer and recent change in weight, the body-mass index (BMI) was significantly associated with colorectal-cancer-risk in men (odds ratio, OR, in highest vs. lowest quintile = 1.7; 95% confidence interval, CI, 1.3-2.3), but not in women (corresponding OR = 0.9; 95% CI, 0.7-1.2). Cases of both gender tended to have higher BMI than controls in adolescence, young adulthood and middle age. Height appeared unrelated to risk. In women, but not in men, WHR was positively associated with risk, independently of BMI (OR for > or = 0.90 vs. < or = 0.81 = 1.6; 95% CI; 1.2-2.1). Thus, excessive weight predicts colorectal-cancer risk in men, whereas abdominal obesity (i.e., a high WHR) represents a more reliable risk indicator in women.