PurposeThe goal of this work was to investigate the oncological outcome of whole pelvis radiotherapy (wpRT) in pathologic pelvic lymph node-positive (pN1) prostate cancer (PCa), evaluate the location of relapse, and identify potential prognostic factors.Patients and methodsAll patients undergoing pelvic lymph node dissection (PLND) since the year 2000 at a single tertiary care center were evaluated. A total of 154 patients with pN1 PCa were treated with wpRT (39 in an adjuvant setting) and 2–3 years of androgen deprivation therapy (ADT). Kaplan–Meier analysis was performed to estimate biochemical recurrence-free survival (bRFS), clinical progression-free survival (cPFS), and prostate cancer-specific survival (CSS). Uni- and multivariate regression analyses were performed to identify prognostic factors.ResultsEstimated bRFS was 67%, cPFS was 71%, and CSS was 96% at 5 years. Median follow-up was 55 months (interquartile range 25–87). Multivariate analysis identified having only 1 positive lymph node, a shorter time between diagnosis and PLND, and older age as independent favorable prognostic factors for biochemical and clinical recurrence. The number of positive lymph nodes was prognostic for CSS (hazard ratio [HR] 1.34, 95% confidence interval 1.17–1.54) and OS (HR 1.22, 95% confidence interval 1.10–1.36). Bone metastases were the most frequent location of PCa relapse (n = 32, 64%).ConclusionsPatients with pN1 PCa treated with wpRT and 2–3 years ADT have an encouraging 5‑year CSS. Understaging of the disease extent may be the most important enemy in definitive pN1 PCa treatment.