Screening for colorectal carcinoma (CRC) was organized for 236 asymptomatic family members in 22 Finnish cancer family syndrome (CFS) kindreds, and 58% (137) of the subjects accepted the invitation. Double-contrast colonography and sigmoidoscopy or colonoscopy were used. In 137 subjects aged 20-65 years, with 3 or more first-degree relatives with CRC, one screening visit showed a colonic neoplasm in 12 (9%) subjects. Two had carcinoma (Dukes A and B), and 10 subjects one or more adenomas. Two of the subjects not attending screening (2%) developed Dukes C colon carcinoma during the study period, and one of them died of cancer. Continued screening of 34 patients with a previously identified CFS showed metachronous colorectal tumours in 12 (35%) cases: 9 operable carcinomas and 9 adenomas within 3 years. The preliminary result of screening on the basis of CFS was encouraging. Effective and continuous screening, however, requires centralized organization. The continued follow-up of identified CFS cases effectively revealed metachronous colorectal tumours at a curable stage, but its benefit was burdened by a high rate of advanced malignancies other than CRC.