The Fracture Risk Assessment Tool (FRAX®) was created to predict major osteoporotic fractures (MOF) and hip fractures in the general population. Whether FRAX accurately predicts fractures in men with prostate cancer is unknown. Our objective was to assess the performance of FRAX for predicting incident fractures in men with prostate cancer. Men from the Manitoba Bone Mineral Density (BMD) Registry (1996–2018) with prostate cancer diagnoses in the 3 years prior to dual-energy X-ray absorptiometry (DXA) were identified. FRAX scores with and without BMD were calculated. From population-based healthcare data we identified incident MOF, hip fracture, any osteoporotic fracture and death from the date of BMD testing to March 31, 2018. Cox regression was performed to estimate hazard ratios (HRs) with 95% confidence intervals (95% CIs) per standard deviation increase in FRAX score. Observed 10-year probability (estimated with competing risk of mortality) was compared with 10-year FRAX-predicted fracture probability to assess calibration. The study population included 684 men with prostate cancer (mean age 74.6 years) and 8608 men without prostate cancer (mean age 65.5 years). FRAX stratified risk for MOF (HR 1.91, 95% CI 1.48–2.45 with BMD;​ HR 1.96, 95% CI 1.43–2.69 without BMD) and hip fracture (HR 3.37, 95% CI 1.90–6.01 with BMD;​ HR 4.58, 95% CI 2.17–9.67 without BMD) in men with prostate cancer. There was no effect modification observed with prostate cancer status or current androgen deprivation therapy. Observed 10-year fracture probability in men with prostate cancer showed good agreement with FRAX with and without BMD included in the calculation (observed/predicted calibration ratios MOF 0.97, hip 1.00 with BMD;​ MOF 0.92, hip 0.93 with BMD). In conclusion, FRAX reliably predicts incident fractures in men with prostate cancer.