BACKGROUND: Early detection of colorectal cancer could reduce cancer-specific mortality. The aim of this trial was to evaluate the effect of faecal occult blood test (FOBT) screening on colorectal cancer mortality in a Swedish population. METHODS: All 68,308 citizens in Göteborg born between 1918 and 1931 were randomized to a screening or a control group at the age of 60-64 years. All were screened two to three times with rehydrated Hemoccult-II. Compliance was 70.0 per cent (23,916 individuals). Those with a positive test result were offered sigmoidoscopy and a double-contrast enema. The primary endpoint was death from colorectal cancer. RESULTS: After a mean of 9 years from the last screening, there was a significant reduction in colorectal cancer mortality in the screening group compared with the control group. The overall risk ratio of death from colorectal cancer was 0.84 (95 per cent confidence interval 0.71 to 0.99). The groups did not differ in incidence of colorectal cancer or in overall mortality. CONCLUSION: FOBT screening significantly reduces colorectal cancer mortality.