It is often difficult to diagnose Crohn's disease because of the numerous clinical symptoms. In a retrospective study from 1963-1975 the initial diagnosis was examined in 101 patients with Crohn's disease. In 22% of the patients the initial diagnosis was correct, in 78% one or more wrong diagnoses were made. The most regular wrong diagnosis was colitis ulcerosa (30%). 41 patients were unnecessarily treated surgically before the correct diagnosis was established. The mean time from the on-set of the symptoms until the correct diagnosis was 3.6 years, the mean time from the first wrong diagnosis to the correct diagnosis, 2.9 years. In the later few years a decrease in wrong diagnoses, an increase in initially correct diagnoses and a shortening of the interval between beginning of symptoms until final diagnosis are recognizable. The possible reasons are discussed.