ObjectiveTo quantify the differences in 5‐year overall survival (OS) between high‐grade (Gleason sum 8–10) incidental prostate cancer (IPCa) patients and age‐matched male population‐based controls, according to treatment type: no active versus active treatment.Materials and MethodsWe relied on the Surveillance, Epidemiology, and End Results (SEER) database (2004–2015) to identify not actively treated and actively treated high‐grade IPCa patients. For each case, we simulated an age‐matched male control (Monte Carlo simulation), relying on Social Security Administration Life Tables (2004–2020) with 5 years of follow‐up. Additionally, we relied on Kaplan–Meier plots to display OS for each treatment type. Multivariable Cox regression models were fitted to predict overall mortality (OM).ResultsOf 564 high‐grade IPCa patients, 345 (61%) were not actively treated versus 219 (39%) were actively treated, either with radical prostatectomy or radiotherapy. Median OS was 3 years for not actively treated high‐grade IPCa patients, with OS difference at 5 years follow‐up of 27% relative to their age‐matched male population‐based controls (37% vs. 64%). Median OS was 8 years for actively treated high‐grade IPCa patients, with OS difference at 5 years follow‐up of 6% relative to their age‐matched male population‐based controls (68% vs. 74%). In the multivariable Cox regression model, active treatment independently predicted lower OM (hazard ratio = 0.6; 95% confidence interval = 0.4–0.8; p < 0.001).ConclusionRelative to Life Tables' derived age‐matched male controls, not actively treated high‐grade IPCa patients exhibit drastically worse OS than their actively treated counterparts. These observations may encourage clinicians to consider active treatment in newly diagnosed high‐grade IPCa patients.