 21,000 men and women, aged 50-64 years, living in the city of Oslo or the county of Telemark are drawn by randomisation approx. 1:5 from the population registry and invited to have a flexible sigmoidoscopy examination. The control group constitutes 79,000 individuals. Those invited for flexible sigmoidoscopy are further randomised 1:1 to bring or not to bring 3 successive stool samples for FOBT on attendance for FS. 