Cytokeratin 17 (CK17), a basal/myoepithelial cell keratin, is a poor prognostic marker for cancers of organs such as the stomach, ovary, and breast as well as a useful diagnostic marker for pancreatobiliary adenocarcinoma. However, its expression pattern and prognostic significance have not been studied in gallbladder adenocarcinoma. We constructed a tissue microarray from samples from 82 consecutive patients with gallbladder adenocarcinoma treated by cholecystectomy at the Kangbuk Samsung Hospital from 2000 to 2011. CK17 expression was examined by immunohistochemistry and correlated with clinicopathologic prognostic factors. CK17 stained the cytoplasm of tumor cells and immunohistochemical interpretation was possible in 77 cases. Among these, 41 (53.2%) were considered positive using a 5% cutoff determined by a receiver operating characteristic curve (area under the curve=0.656, P=0.021). CK17 expression was associated with poor tumor differentiation (P<0.001), high pT stage (P<0.001), presence of distant metastasis (P=0.036), and low disease-specific survival rate (P<0.001). These results indicate that CK17 can be used as a marker for poor prognosis for gallbladder adenocarcinoma.