The prognosis and the occurrence of premalignant conditions were studied in 249 patients with colorectal carcinoma, diagnosed before the age of 40 years, between 1970 and 1979, in Finland. The aim was to evaluate the possibilities for prevention and screening of colorectal carcinoma in young people. The 5-year survival (41%) corresponded to that observed generally in colorectal carcinoma. The therapeutic delay (mean, 8.6 months) was not longer in the advanced stages (Duke's C, D), which comprised 53% of all, than in the localized stages. A premalignant condition occurred in 46 patients (18.5%): familial adenomatous polyposis coli in 18 (7.2%), ulcerous colitis in 11 (4.4%), cancer family syndrome in 9 (3.6%), and miscellaneous conditions in 8 (3.2%) patients. The younger the patient, the more often a premalignant condition was found. Nearly half of the high-risk patients could have been identified earlier. The findings suggest that more emphasis should be placed on the identification, family screening, and treatment of the conditions predisposing to colorectal cancer.