Background: While the 5-year survival rate for local and regional prostate cancer is nearly 100%, it decreases dramatically for advanced tumours. Accessibility to health care is an important factor for cancer prognosis. The U.S. Military Health System (MHS) provides universal health care to its beneficiaries, reducing financial barriers to medical care. However, whether the universal care translates into improved survival among patients with advanced prostate cancer in the MHS is unknown. In this study, we compared the MHS and the U.S. general population in survival of patients with advanced prostate cancer (stages III and IV). Methods: The MHS patients (N = 5379) were identified from the Department of Defense’s (DoD) Automated Central Tumor Registry (ACTUR). Patients in the U.S. general population (N = 21,516) were identified from the Surveillance, Epidemiology, and End Results (SEER) programme. The two populations were matched on age, race, and diagnosis year. Results: The ACTUR patients exhibited longer 5-year survival than the matched SEER patients (HR = 0.74, 95% CI = 0.67–0.83), after adjustment for the potential confounders. The improved survival was observed for ages 50 years or older, both White patients and Black patients, all tumour stages and grades. This was also demonstrated despite the receipt of surgery or radiation treatment. Conclusions: MHS beneficiaries with advanced prostate cancer had longer survival than their counterparts in the U.S. general population.