We examined the immunohistochemical expression of sialosyl-Tn antigen in the colorectal cancer tissues of 116 patients who underwent curative resection to determine the association between patient prognosis and the expression of sialosyl-Tn in two different tissues: carcinoma and transitional mucosa. Negative or positive expression of sialosyl-Tn in the carcinoma and transitional mucosal tissues were denoted as CA- or CA+ and TM- or TM+, respectively. Patients were classified into one of four groups: CA-/TM-, CA-/TM+, CA+/TM-, and CA+/TM+. CA-/TM- was observed in 13 patients and CA-/TM+, CA+/TM-, or CA+/TM+ was observed in 103 patients. The difference in five-year survival between the CA-/TM- group and all the other groups was statistically significant (P = 0.0457), and multivariate analysis showed that sialosyl-Tn expression in at least one of the two tissues was an independent prognostic factor. We conclude that the evaluation of sialosyl-Tn expression in carcinoma as well as transitional mucosa is useful for predicting survival in colorectal cancer patients.