['Current research is inconclusive regarding the effect of obesity on outcomes after a prostate cancer diagnosis. The objective of this study was to examine associations between obesity and the risks of developing metastasis or prostate cancer-specific mortality in a population-based cohort of men with prostate cancer.', 'Seven hundred fifty-two middle-aged men with prostate cancer who were enrolled in a case-control study and remain under long-term follow-up for disease progression and mortality formed the study cohort. Body mass index (BMI) in the year before diagnosis was obtained at the time of initial interview. Cox proportional hazards models were used to estimate hazard ratios (HRs) and 95% confidence intervals (95% CIs) of prostate cancer metastasis and mortality associated with obesity, controlling for age, race, smoking status, Gleason score, stage at diagnosis, diagnostic prostate-specific antigen level, and primary treatment.', 'Obesity (BMI >or=30 kg/m(2)) was associated with a significant increase in prostate cancer mortality (HR, 2.64; 95% CI, 1.18-5.92). Among men who were diagnosed with local- or regional-stage disease, obesity also was associated with an increased risk of developing metastasis (HR, 3.61; 95% CI, 1.73-7.51). Associations generally were consistent across strata defined by Gleason score (2-6 or 7 [3 + 4] vs 7 [4 + 3] or 8-10), stage (local vs regional/distant for mortality), and primary treatment (androgen-deprivation therapy use: yes vs no).'] Is obesity associated with increased risks of prostate cancer metastasis and death after initial cancer diagnosis in middle-aged men?