Overweight and obesity are linked with several chronic diseases, including colorectal cancer, among men, but results among women are equivocal. Previous evidence suggests that menopausal status, postmenopausal hormone use, and family history of cancer may modify the link between adiposity and colorectal cancer. In data from two population-based case-control studies (cases: 1,292 males and 1,404 females; controls: 1,465 males and 1,203 females) in Ontario and Newfoundland, Canada, we examined the link between colorectal cancer and body mass index (BMI) at two reference periods (BMI 2 years prior and BMI at age 20 years), weight gain since age 20 years, and height. Based on recent BMI indices among men, obesity (BMI >/=30 kg/m(2)) was associated with an 80% [95% confidence interval (95% CI), 1.43-2.27] increased risk of colorectal cancer relative to a normal BMI (18.5-24.9 kg/m(2)). The same comparison for BMI at age 20 years suggested a 94% increased risk of colorectal cancer (95% CI, 1.19-3.16). Odds ratios were similar among subgroups of men with and without a clinically defined familial risk of cancer (according to the Amsterdam or revised Bethesda criteria for Lynch syndrome). Associations were moderately stronger for cancer of the colon than cancer of the rectum. Among women, BMI and weight gain were not linked with colorectal cancer; the null associations were persistent in subgroups of familial risk of cancer, menopausal status, estrogenic status, and subsite. Tall height (>1.75 m), however, was linked with increased risk of colorectal cancer among women (odds ratio, 2.27; 95% CI, 1.46-3.59) but not among men. This study suggests that obesity is associated with increased risk of sporadic and Lynch syndrome-related colon and rectal cancers among men but not among women, whereas height is directly linked with all such cancers among women but not among men.