Recent studies have shown that microsatellite instability (MSI) play an important role in the development of various types of cancer. To clarify the clinicopathologic significance of MSI in colorectal carcinoma (CRC), the presence of MSI was examined in 54 Japanese cases of CRC using the polymerase chain reaction-based method. The incidence of MSI in CRC cases was 13 out of 54 cases (24%). CRC with MSI also showed a significant tendency not to have lymph node metastasis (P<0.05), although neither the survival nor the prognosis of the cases examined in this study were available due to the short period of follow-up. The present study showed that the incidence of MSI in Japanese CRC was 24% and suggests that CRC with MSI may behave in a less malignant manner.