Background: A recent randomized controlled trial demonstrated that radiation therapy to the prostate improves overall survival for men with newly diagnosed metastatic prostate cancer with a low metastatic burden. Most patients in this trial had bony metastases (stage M1b). The benefit of prostate-directed radiation therapy for men with metastases limited to non-regional lymph nodes (stage M1a) is unknown. We investigated the association between prostate-directed radiation therapy and overall survival for men with M1a prostate cancer. Methods: We identified 2,079 men from the National Cancer Database who were newly diagnosed with M1a prostate adenocarcinoma from 2004 through 2014 and had data on the use of androgen deprivation therapy, chemotherapy, and radiation therapy. Median follow-up was estimated using the reverse Kaplan-Meier method. The association between radiation therapy to the prostate and overall survival was examined using multivariable Cox proportional hazards regression analysis. Results: Overall, 12.7% (264) of patients received radiation therapy to the prostate. Median follow-up was 4.6 years (95% confidence interval 4.3-4.8 years). On multivariable analysis, when accounting for the use of androgen deprivation therapy and chemotherapy, Gleason grade group, clinical tumor and nodal stage, and prostate-specific antigen level at diagnosis, the use of radiation therapy to the prostate was associated with a significant improvement in overall survival (adjusted hazard ratio 0.60, 95% confidence interval 0.49-0.74, P<0.001). Adjusted median overall survival was 3.3 years for patients who did not receive radiation therapy to the prostate compared to 5.5 years for patients who did. Conclusions: Similar to newly diagnosed M1b prostate cancer with a low metastatic burden, patients with M1a prostate cancer may also derive a significant overall survival benefit from receiving radiation therapy to the primary prostate tumor. The use of prostate-directed radiation therapy for M1a patients should be further investigated.