Gallbladder carcinoma is an aggressive type of neoplasm difficult to cure by conventional procedures. Because of the lack of reliable markers for assessing the prognosis, this retrospective study was designed to investigate the prognostic significance of MK-1 overexpression in human carcinoma of the gallbladder. Immunohistochemical staining using monoclonal antibody FU-MK-1 (MK-1 antigen) was performed on paraffin-embedded tissues from 63 patients who had undergone surgical resection for gallbladder carcinoma. Expression of MK-1 was found in 50 (79%) of 63 tumor samples. All 21 papillary and 12 of 13 well-differentiated tubular adenocarcinomas but only 1 of 8 poorly differentiated adenocarcinomas were positive for FU-MK-1. Multivariate analysis showed that only MK-1 expression was an independent prognostic marker (P = .0473), and Kaplan-Meier curves showed that MK-1 expression was significantly related to increased overall survival (P < .0001). These results suggest that MK-1 expression is a prognostic marker in gallbladder carcinoma.