The objective of this study was to investigate the association between constipation or laxative use and the risk of colorectal cancer in Japanese men and women. In 1990, we delivered a self-administered questionnaire to 41670 subjects who were 40-64 years old. During the seven years of follow-up, 251 incident cases of colorectal cancer were documented. Constipation was defined as a bowel movement frequency of less than daily. The multivariate relative risk (RR) of colorectal cancer for constipated subjects compared with those with daily bowel movements was 1.35 (95% Confidence Interval: 0.99-1.84). The RR for laxative users over non-users was 1.31 (0.88-1.95), and for frequent users (twice a week or more) it was 2.75 (1.48-5.09). When colorectal cancers were divided into colon cancers or rectal cancers, a significant association was found with colon cancer alone. Our results support the hypothesis that constipation or laxative use increases the risk of colon cancer.