To evaluate certain risk and protective factors for colon cancer in our population, we conducted a paired case-control study where cases were all people diagnosed with colon cancer who were registered at the Cancer Data Exchange Systems of the Community of Madrid between January 1995 and December 1996, and controls were randomly taken from electoral lists. The study population consisted of 424 persons. Using SPSS for Windows, variables were adjusted by multiple logistic regression. The results indicate that lack of physical exercise is associated with an increased risk of colon cancer, with an odds ratio (OR) of 2.8 (95% confidence interval (CI) 1.28-6.21) as compared with moderate activity 1-2 days a week. The risk decreases linearly with increasing physical exercise, and this association remains after stratifying the analysis for the existence of constipation. The consumption of is associated with a reduced risk of colon cancer in constipated patients, with an OR of 0.094 (0.014-0.639), as is aspirin use, with an OR of 0.980 (0.898-0.999). These results were obtained after adjusting all the ORs for diet, smoking, alcohol consumption, family history and socio-demographic factors such as marital status and educational level.