The aim of cancer rehabilitation is to enable patients to attain and maintain optimal physical, psychological and social functioning. We evaluated the effect on health behavior, BMI and self-rated health of a residential psychosocial rehabilitation course for cancer patients. Material and methods. Patients with a primary cancer of the breast, prostate, colon or rectum were randomized to either a six-day multi-focus psychosocial residential rehabilitation intervention that included lectures, discussions and peer group discussions on issues related to treatment and life with cancer or to usual care. The end points were changes in smoking, alcohol consumption, physical activity, body mass index and self-rated health between baseline and follow-up after one and six months. The primary analyses included all participants who received their allocated condition. The two follow-up times were analyzed separately in general linear and logistic regression models for continuous and dichotomous outcomes, respectively. The analyses were adjusted for baseline outcome score, cancer site, time since diagnosis, age and education. Results. Of the 507 participants who were randomly assigned, 452 were included in the analysis, of whom 404 completed the one month and 394 completed the six month assessment. The intervention group showed slightly more positive changes in health behavior, BMI and self-rated health than the usual care group, but the differences between the groups were small and not significant. Discussion. Participation in a six-day cancer rehabilitation course did not significantly influence health behavior, BMI or self-rated health among cancer patients.