Background: Approximately 15% of the US population does not have health insurance. The objective of this study was to evaluate the impact of insurance status on tumor characteristics and treatment selection in patients with prostate cancer. Materials and Methods: We identified 20,393 patients younger than 65 years with prostate cancer in the 2010–2011 SEER database. Multivariable logistic regression analysis tested the relationship between insurance status and 2 end points: (1) presenting with low-risk prostate cancer at diagnosis and (2) receiving local treatment of the prostate. Locally weighted scatterplot smoothing methods were used to graphically explore the interaction among insurance status, use of local treatment, and baseline risk of cancer recurrence. The latter was defined using the Stephenson nomogram and CAPRA score. Results: Overall, 18,993 patients (93%) were insured, 849 (4.2%) had Medicaid coverage, and 551 (2.7%) were uninsured. At multivariable analysis, Medicaid coverage (odds ratio [OR], 0.67; 95% CI, 0.57, 0.80; P<.0001) and uninsured status (OR, 0.57; 95% CI, 0.46, 0.71; P<.0001) were independent predictors of a lower probability of presenting with low-risk disease. Likewise, Medicaid coverage (OR, 0.72; 95% CI, 0.60, 0.86; P=.0003) and uninsured status (OR, 0.45; 95% CI, 0.37, 0.55; P<.0001) were independent predictors of a lower probability of receiving local treatment. In uninsured patients, treatment disparities became more pronounced as the baseline cancer recurrence risk increased (10% in low-risk patients vs 20% in high-risk patients). Conclusions: Medicaid beneficiaries and uninsured patients are diagnosed with higher-risk disease and are undertreated. The latter is more accentuated for patients with high-risk prostate cancer. This may seriously compromise the survival of these individuals.