This paper deals with the clinical history, the histopathological and TEM features of a case of intestinal spirochaetosis associated with ulcerative colitis and tubular adenomas of the colon. It is the fifth described case of intestinal spirochaetosis in Sweden, and the first in the literature in which a complete colonoscopy with multiple biopsies has been performed. Intestinal spirochaetosis might lead to minor complaints as distension and vague abdominal discomfort, as in this case, but also to more prominent symptoms such as diarrhoea. Heavy infestation of the gut surface epithelium by spirochaetes was seen in the total colon, but was not found in the distal ileum.