Objective To assess the strength of the evidence indicative of prostate cancer (PCa) progression as the adjudicated cause of death, according to age at death and PCa risk category. Patients and Methods Using data from the Prostate Cancer data Base Sweden, we identified a study frame of 5543 men with PCa registered as the cause of death according to the Cause of Death Register. We assessed the evidence of PCa progression through a review of healthcare records for a stratified sample of 495/5543. We extracted data on prostate‐specific antigen levels, presence of metastases on imaging, and PCa treatments, and quantified the evidence of disease progression using a points system. Results Both no evidence and moderate evidence for PCa progression was more common in men aged >85 years at death than those aged <85 years (29% vs 14%). Among the latter, the proportion with no evidence or moderate evidence for PCa progression was 21% for low‐risk, 14% for intermediate‐risk, 8% for high‐risk, and 0% for metastatic PCa. In contrast, in men aged >85 years, there was little difference in the proportion with no evidence or moderate evidence of PCa progression between PCa risk categories; 31% for low‐risk, 29% for intermediate‐risk, 29% for high‐risk, and 21% for metastatic PCa. Of the 5543 men who died from PCa, 13% (95% confidence interval 5–19%) were estimated to have either no evidence or moderate evidence of PCa progression. Conclusions Weak evidence for PCa progression as cause of death was more common in older men with PCa and in those with low‐risk PCa. This has implications for interpretation of mortality statistics especially when assessing screening and early treatment of PCa because the beneficial effect of earlier diagnosis could be masked by erroneous adjudication of PCa as cause of death in older men, particular those with localised disease at diagnosis.