Objectives : A hospital-based case-control study was conducted to evaluate the role of obesity in the development of colorectal cancer. Methods : Three hundred and twenty four histologically confirmed female colorectal cancer cases and 26,998 non-cancer controls were selected from patients invited to the Aichi Cancer Center, Nagoya, Japan between 1989 and 1995. Information concerning demographic factors, medical history, family medical history, reproductive factors and dietary factors were obtained from self-administered questionnaires and medical records. The effects of weight and body mass index to colorectal cancer were examined using multiple logistic regression to control for other risk factors. Results : There was no significant association between female colorectal cancer and obesity. Heavier weight adjusted for height or body mass index did not increase the risk of colorectal cancer. Conclusions : These results suggest that there is no association between colorectal cancer risk and obesity in women.