In five (6 per cent) of 78 consecutive patients treated with an anterior resection for rectal carcinoma, a stenosis of the sigmoid colon just above the anastomosis was observed. Four patients had received preoperative radiotherapy over a period of 1 week to a total dose of 25.5 Gy and one patient had received postoperative radiotherapy (60 Gy) over a total of 8 weeks. The length of the stenosis varied from 4 to 120 cm. Two patients subsequently underwent reoperation with an abdominoperineal resection and three patients with a Hartmann procedure. In all patients the inferior mesenteric artery had been ligated close to the aorta. It is proposed that the stenosis may have been due to insufficient circulation in the marginal artery. This insufficiency may have been aggravated by the irradiation, as the retained part of the sigmoid colon was partly included in the irradiation target.