SummaryThe occurrence of ulcerative colitis in Finland has been determined with the aid of an indiscriminate series comprising all patients hospitalized in Finland in 1967. The total incidence is 4.8 per 100,000 inhabitants; due to potential errors in the methods, however, this should be regarded as an imprecise estimate. No difference between the incidences in men and in women was observed. The incidence was highest among young adults and in the urban population. A not inconsiderable number contracted ulcerative colitis at advanced ages. The value and limitations of the figures are discussed.