The possibility of early superficial Crohn's disease should be considered when mucosal irregularities without transmural abnormalities are seen in the distal 15 cm of the ileum in young patients with protracted symptoms of abdominal pain and diarrhoea. Radiologic assessment of the small bowel is improved using the barium/air double contrast technique and in this study mucosal abnormalities were categorised as a 'mucosal nodularity pattern', an 'abnormal mucosal fold pattern', and a 'specks of barium pattern'. None of the 21 patients followed prospectively for four to seven years developed established criteria for Crohn's disease, or any other chronic progressive disease of the small bowel. Colon examinations were normal. In comparison 26 patients with histologically proven Crohn's disease of the ileum were studied retrospectively and no similar clinical or radiologic characteristics were present. It is concluded, therefore, that such isolated superficial lesions are not pathognomonic and are not early indicators of Crohn's disease or any other chronic progressive disease of the small bowel.