Randomized data from SWOG 8794 and EORTC 22911 confirm the benefit of post-operative radiation therapy (RT) for selected patients with pT3 prostate cancer (CaP) after radical prostatectomy (RP). However, data regarding the potential benefit of RT for patients post-RP with positive lymph node (+LN) involvement are limited. We analyzed the Surveillance Epidemiology End Results (SEER) registry for population-based data on efficacy of post-operative RT for +LN patients after RP. As LN data have only been captured by SEER since 1988, we analyzed data for 1988–1992, with specific attention to 10-year relative survival (defined as observed survival divided by the survival of a gender-, age- and race-matched population cohort without disease). Specifically analyzed were data for 1921 patients with nonmetastatic prostate cancer who underwent surgery alone, or surgery followed by RT, and who had +LNs documented. SEER does not code the interval between surgery and RT, so the ratio of patients receiving salvage versus adjuvant therapy is unknown. Using follow-up data through 2002, post-diagnosis survival was examined by number of +LNs. There was no significant relative survival benefit for +LN patients receiving post-operative RT (χ2P=0.270). These data do not support routine use of post-operative RT for patients with +LNs in the surgical specimen.