Immunohistochemical expression of sialyl Tn antigen (STn), previously claimed to be a prognostic factor in colorectal cancer, was evaluated in 239 patients with colorectal adenocarcinoma. Formalin-fixed, paraffin-embedded specimens were stained with the monoclonal antibody C1282. STn immunoreactivity was seen in 189 of 239 tumors (79%). There was no significant correlation between STn immunoreactivity and Dukes stage, tumor location, histological type or gender. However, STn was significantly more often expressed in younger patients. There was so significant difference in survival between STn-negative patients (median survival 68 months) and STn-positive patients (median survival 79 months). In a Cox multivariate analysis, Dukes stage was the strongest predictor of outcome, followed by the age of the patient, whereas STn did not provide any prognostic information.