Disialosyl globopentaosylceramide (DSGb5) is a ganglioside originally isolated from renal cell carcinoma (RCC) tissue that has been associated with RCC metastasis. However, in prostate cancer, the expression of DSGb5 has not yet been fully assessed. In this study, we investigated DSGb5 expression in prostate tissues and the relationship between DSGb5 expression and clinicopathological characteristics of prostate cancer patients. Methods: A total of 130 patients who underwent radical prostatectomy (RP) at our hospital between January 2005 and December 2007 were analyzed in this study. The expression of DSGb5 in prostatectomy specimens was examined by immunohistochemical analysis with monoclonal antibody 5F3 (anti-DSGb5). Associations between 5F3 expression and clinicopathological findings were investigated and the factors that affected PSA failure-free survival were assessed by Kaplan-Meier analysis and a Cox regression model. Results: When immunoreactivities of 5F3 were measured, negative to strong staining was observed in prostate cancer tissue, whereas strong staining was observed in benign prostate glands. These expression patterns suggest that DSGb5 may act as a differentiation antigen in cancerization. The PSA failure-free survival was significantly higher in the 5F3 intact expression group than in the 5F3 reduced expression group (log-rank P=0.0220). On multivariate analysis, 5F3 intact expression showed significantly worse PSA failure-free survival following RP. Conclusions: 5F3 expression reflects the clinical and pathological features of prostate cancer and is correlated with the outcomes following RP. Further studies are necessary to clarify the functional roles of DSGb5 and establish a novel biomarker for prostate cancer.