Abstract Purpose: The cancer-testis antigen NY-ESO-1 is expressed by >40% of advanced epithelial ovarian cancers and is a promising immunotherapeutic target. In this study, we describe the effects of vaccination with the HLA-A*0201–restricted NY-ESO-1b peptide on patients with epithelial ovarian cancer in high-risk first remission. Experimental Design: After primary surgery and chemotherapy, high-risk epithelial ovarian cancer patients in first clinical remission received NY-ESO-1b peptide and Montanide every 3 weeks for five vaccinations. Tumor expression was evaluated by immunohistochemistry. Toxicity was monitored using National Cancer Institute Common Toxicity Criteria Scale Version 2. NY-ESO-1 specific humoral immunity (ELISA), T-cell immunity (tetramer and ELISPOT), and delayed-type hypersensitivity were assessed on weeks 0, 1, 4, 7, 10, 13, and 16. Results: Treatment-related adverse events included grade 1 fatigue, anemia, pruritus, myalgias, and hyperthyroidism and grade 2 hypothyroidism. There were no grade 3/grade 4 adverse events. Three of four patients (75%) with NY-ESO-1–positive tumor showed T-cell immunity by tetramer (0.6-9.5%) and ELISPOT (range, 35-260 spots). Four of five patients (80%) with NY-ESO-1–negative tumor showed T-cell immunity by tetramer (1.0-12.1%) and/or ELISPOT (range, 35-400 spots). With a median follow-up of 11.3 months, six of nine patients (67%) have recurred, with a median progression-free survival of 13 months (95% confidence interval, 11.2 months–not reached). Three of nine patients remain in complete clinical remission at 25, 38, and 52 months. Conclusion: Vaccination of high-risk HLA-A*0201–positive epithelial ovarian cancer patients with NY-ESO-1b and Montanide has minimal toxicity and induces specific T-cell immunity in patients with both NY-ESO-1–positive and NY-ESO-1–negative tumors. Additional study is warranted.