Summary1. Carcinoma of the sigmoid colon occurred mostly between 40 and 80 years of age, with the highest incidence between 60–70 years. The disease affected 3 patients in their twenties. Females are slightly more commonly involved.2. Two‐thirds of the patients had a typical non‐urgent mode of presentation. The barium enema occasionally produced a false negative result. The remaining one‐third presented either with acute large bowel obstruction or with perforation of the tumour. When perforation occurs, it causes an abscess (or intense inflammatory reaction) which may remain localized, burst into the peritoneal cavity, or discharge into the bladder and produce a vesico‐colic fistula.3. Sixteen per cent, of cases were not resected. Multiple peritoneal metastases, a large fixed mass (sometimes partly inflammatory) and poor condition of the patient were responsible.4. Palliative resection was performed in about 25 per cent, of cases. There were 3 deaths after resection. Two survived unexpectedly. One had a large sub‐serosal plaque of malignant tissue in relation to the primary tumour and associated with peritoneal free fluid; the other had small nodules on the surface of the small bowel, thought to be secondary deposits, but later shown to be carcinoid tissue.5. Curative resections were performed in 59 per cent, of the patients. Two of the 86 patients so treated died in the post‐operative period. A further patient developed a faecal fistula and required a colostomy to close it. A total of 51 patients were treated five years or more ago, and 44 (86 per cent.) survived. Five of the 7 failures had curative excisions after earlier treatment for acute large bowel obstruction. There have been 3 late deaths from recurrence, all intra‐abdominal.6. Large bowel obstruction complicated 36 of the patients. Caecostomy proved a satisfactory method of overcoming the obstruction, and was performed on 16 occasions. Resection was performed in 14 of the 16 patients, and an anastomosis in 13. Colostomy was an alternative method of decompressing the bowel, but did not appear to have any advantage over caecostomy. Immediate resection was used on occasions, but its place appeared limited. The long term prognosis of obstructed patients is only fair with 5 of 21 patients treated five years or more ago surviving.7. Perforation with abscess formation is a formidable complication because it complicates subsequent removal. If the abscess should discharge into the bladder, one‐stage resection is not only a satisfactory operation but is followed by good 5‐year survivals.8. A total of 80 patients were referred 5 years or more ago and 46 survived at least that period, an absolute five‐year survival rate of 57.5 per cent. Of 22 patients seen ten years or more ago, 8 survived, an absolute ten‐year survival of 36 per cent.9. It is concluded that one‐stage partial sigmoid colectomy with end‐to‐end anastomosis, without mobilization of the splenic flexure or rectum, and completed. without drainage or post‐operative antibiotics is the treatment of choice for