We report four cases of rectal spirochaetosis, one in an active male homosexual. One of the heterosexual patients was referred to the genitourinary clinic by a general surgeon after spirochaetes had been found on histopathological examination of a rectal biopsy specimen. We doubt that most of our cases represent sexual transmission of spirochaetosis, or that the condition causes disease in most people. Rectal spirochaetosis possibly occurs only when the normal flora of the gut are disturbed for other reasons. Most of our patients became asymptomatic after nonspecific treatment, although metronidazole appears to be specific.