Cancer-testis (CT) antigens are immunogenic proteins expressed in normal gametogenic tissues and in different types of tumors. CTSP-1 is a CT antigen frequently expressed in prostate tumors, and capable of eliciting humoral response in prostate cancer patients. Here, we analyzed the presence of anti-CTSP-1 antibodies in 147 patients with localized prostate cancer and determined its prognostic value for predicting biochemical-recurrence after radical prostatectomy. Anti-CTSP-1 antibodies were detected in 25% of the patients and a significant correlation (p = 0.017) between CTSP-1 protein expression and the presence of specific humoral response was observed. No association was found between the presence of antibodies and the pathological variables analyzed. On univariate analysis, patients without antibodies against CTSP-1 had a lower biochemical-recurrence free survival than did those with anti-CTSP-1 antibodies, although the difference between the groups was not statistically significant (57 vs. 75%, p = 0.075). However, the presence of antibodies against CTSP-1 was significantly associated with a better prognosis in patients with higher Gleason score (36 vs. 80%, p = 0.028). On multivariate analysis, antibodies against CTSP-1 were associated with a better prognosis (Hazard ratio = 0.41, 95% IC 0.18–0.90 p = 0.039), being the third most powerful prognostic factor among Gleason score and preoperative PSA levels. CTSP-1 should be considered a promising candidate for prostate cancer immunotherapy, since it is frequently expressed in prostate tumors and capable of eliciting humoral immune response in prostate cancer patients. Our results also suggest that humoral response against CTSP-1 could be used as a prognostic marker, especially among patients with a high Gleason score. © 2008 Wiley-Liss, Inc.