PURPOSE: Little is known about the toxicity of additional pelvic lymph node irradiation in men receiving intensity modulated radiation therapy (IMRT) for prostate cancer. The aim of this study was to compare patient-reported outcomes after IMRT to the prostate only (PO-IMRT) versus the prostate and pelvic lymph nodes (PPLN-IMRT). METHODS AND MATERIALS: Patients who received a diagnosis of high-risk or locally advanced prostate cancer in the English National Health Service between April 2014 and September 2016 who were treated with IMRT were mailed a questionnaire at least 18 months after diagnosis. Patient-reported urinary, sexual, bowel, and hormonal functional domains on a scale from 0 to 100, with higher scores indicating better outcomes, and generic health-related quality of life were collected using the Expanded Prostate Cancer Index Composite 26-item version and EQ-5D-5L. We used linear regression to compare PPLN-IMRT versus PO-IMRT with adjustment for patient, tumor, and treatment characteristics. RESULTS: Of the 7017 men who received a questionnaire, 5468 (77.9%) responded; 4196 (76.7%) had received PO-IMRT and 1272 (23.3%) PPLN-IMRT. Adjusted differences in the Expanded Prostate Cancer Index Composite 26-item version domain scores were smaller than 1 (P always >.2), except for sexual function, with men who had PPNL-IMRT reporting a lower mean score (adjusted difference, 2.3; 95% confidence interval, 0.9-3.7; P = .002). This did not represent a clinically relevant difference. There was no significant difference in health-related quality of life (P = .5). CONCLUSIONS: Additional pelvic lymph node irradiation does not lead to clinically meaningful increases in the toxicity of IMRT for prostate cancer according to patient-reported functional outcomes and health-related quality of life.