OBJECTIVE:To assess whether obesity is associated with progression to metastasis, prostate cancer-specific mortality (PCSM), and all-cause mortality (ACM), in patients with non-metastatic castration-resistant prostate cancer (non-mCRPC). At the population level, obesity is associated with prostate cancer mortality; however, some studies have found that higher body mass index (BMI) is associated with better long-term prostate cancer outcomes amongst men with mCRPC. PATIENTS AND METHODS:We identified 1 192 patients with non-mCRPC from the Shared Equal Access Regional Cancer Hospital (SEARCH) database. BMI was calculated from height and weight abstracted from the medical records at the time closest to but prior to CRPC diagnosis and categorised as underweight (<21 kg/m2 ), normal weight (21-24.9 kg/m2 ), overweight (25-29.9 kg/m2 ), and obese (≥30 kg/m2 ). Competing risks regression and Cox models were used to test associations between obesity and progression to metastasis, PCSM, and ACM, accounting for confounders. RESULTS:Overall, 51 (4%) men were underweight, 239 (25%) were normal weight, 464 (39%) were overweight, and 438 (37%) were obese. In adjusted analysis, higher BMI was significantly associated with reduced ACM (hazard ratio [HR] 0.98, P = 0.012) but not PCSM (HR 1.00, P = 0.737) or metastases (HR 0.99, P = 0.225). Likewise, when BMI was treated as a categorical variable in adjusted models, obesity was not associated with PCSM (HR 1.11, P = 0.436) or metastases (HR 1.06, P = 0.647), but was associated with decreased ACM (HR 0.79, P = 0.016) compared to normal weight. No data were available on treatments received after CRPC diagnosis. CONCLUSIONS:Amongst patients with non-mCRPC obesity was associated with better overall survival. Although this result mirrors evidence from men with mCRPC, obesity was not associated with prostate cancer outcomes. Larger studies are needed to confirm these findings.