Anal and perianal lesions in Crohn's disease such as fistulae, fissures, abscesses and proliferative ulcerous proctitis are often misinterpreted and consequently unsatisfactorily treated. They always indicate a florid intestinal attack or a relapse after previous intestinal resection. Out of 153 patients with Crohn's disease in the last 11 years we have had 59 cases (= 38.6%) with a history of anal changes or such changes were demonstrable on admission to hospital. Only after subtle diagnosis in which the nature and extent of these complications and the location of the intestinal disease focus are determined, the most promising therapy, after all possibilities of conservative treatment have been exhausted, is intestinal resection. Local surgical measures which would often endanger continence, are reserved for the individual case.