SummaryForty‐six patients with primary carcinoma arising between the hepatic and splenic flexures of the colon were studied to relate the preoperative symptoms, the width of the lumen of the colon at the site of the lesion on barium‐enema examination, and the surgical pathology of the neoplasm. Rectal bleeding was frequently produced by lesions which had not extended beyond the wall of the bowel. Compensatory hypertrophy of the colonic musculature proximal to the lesion delays the onset of symptoms. Obstructive symptoms indicated one of two situations: 1) tumor was confined to the colon but had narrowed the lumen to a channel 6 mm wide or less; 2) tumor had grown beyond the serosa of the bowel to involve adjacent structures with inflammatory or neoplastic adhesions.