PURPOSE: Epidemiologic studies have indicated that the use of nonsteroidal anti-inflammatory drugs, which inhibit cyclooxygenase activity, reduce the risk of colorectal cancer. In addition, several studies have demonstrated the increased expression of cyclooxygenase-2 (COX-2) in human colorectal cancer tissues. However, the role of COX-2 in colorectal cancer has not been fully established. The aim of this study was to clarify the clinicopathologic significance of COX-2 expression in human colorectal cancer. METHODS: We performed immunohistochemical straining for COX-2 expression in 124 human colorectal cancer specimens. COX-2 expression was then compared with clinicopathologic factors and survival outcomes. RESULTS: COX-2 was expressed in the cytoplasm of the cancer cells. COX-2 expression was noted in 86.3% of the cancer patients and significantly correlated with the histologic type. The depth of invasion, tumor size, lymph node metastasis and stage were not correlated with COX-2 expression. Multivariate analysis for the factors associated with survival showed that serum CEA, size, depth and lymph node involvement correlated with survival, but COX-2 expression had no correlation. CONCLUSION: These data suggest that COX-2 expression in primary lesion of colorectal cancer may not be a useful marker for evaluating prognosis. However, further studies are necessary for identification of the roles in colorectal carcinogenesis.