PURPOSE: Many reports have described significantly lower survival rates for patients with obstructing colorectal cancer than for patients with non-obstructing colorectal cancer. The aim of this retrospective study was to assess the long-term prognosis of patients with obstructing carcinomas of the left colon and rectum and to identify the clinical and pathologic characteristics that affect the prognosis. METHODS: From June 1996 to October 2003, 46 patients with obstructing left colon and rectal cancer underwent curative surgery (case group), and from the patients with non- obstructing left colon and rectal cancer who had curative surgery, 48 patients with clinicopathologic characteristics similar to those of the case group were selected and matched as a control group. A comparative analysis of demographic, clinical, and pathologic characteristics, the recurrence rate, and the long-term survival rate between these two groups was done. RESULTS: Emergency operations were done more frequently for obstructing cancer than for non-obstructing cancer (P=0.0001), and more patients with obstructing cancer presented to non-specialists (P=0.0001). The overall recurrence rate was significantly higher in obstructing cancer patients than in non-obstructing cancer patients. Further, the 5-year overall and the disease-free survival rates were significantly lower in obstructing cancer patients when examining either overall patient outcome or stage-III patients outcome. CONCLUSIONS: The long-term prognosis of patients with obstructing carcinomas of the left colon and rectum is poor. We suggest that the poor general condition of patients with obstructing cancer, the increased number of emergency operations involving those patients, and more patients with obstructing cancer presenting to non-specialists may contribute to poor long-term prognosis for obstructing cancer patients.