Objective To study the causes, diagnosis and treatment of the spontaneous perforation of sigmoid colon(SPSC). Methods The clinical data of 11 patients with SPSC admitted into our hospital from January. 1984 to September. 2000 were analyzed retrospectively. Results All the 11 cases of SPSC were proved by operation. Among them, 4 cases had chronic constipation history, 1 case complicated with mild proctoptoma before operation and the other 6 cases had no special records. 9 cases were misdiagnosed as perforation of acute appendicitis, perforation of upper gastroenteric tract, perforation of colon carcinoma, inflammatory perforation or fecal mass perforation. 2 cases recovered after repairing operation; of 9 cases underwent colostomy and other procedure, 7 cases recovered and colostomy closure was done 2-3 months after operation. 2 cases died after operation. Conclusions The occurrence of SPSC is closely related to the configuration and position of the patient's sigmoid colon. Increase of intra-abdominal pressure and intra-intestinal pressure are the predisposing causes of the disease. This disease has no special clinical manifestation. The key to diagnosis is a full knwledge of the disease before operation. The main treatment is operation. The mode of operation is determined according to patient's age, general condition, severity of abdominal pollution, attacking time. The best mode of operation is to repair and close the perforation or to resect and anastomose the bowel and colostomy.