A case of ruptured colon and massive faecal contamination of the peritoneal cavity after a difficult bowel movement is presented. A perforated peptic ulcer was suspected but a rupture of the rectosigmoid colon was found at operation. Surgical management included resection of the affected colon, proximal colostomy and closure of the distal end of the bowel. Definitions of spontaneous rupture and stercoral perforation of the colon are given, and the possible aetiological factors in and management of these rare cases are discussed.