Background <p>Studies on the association between obesity and mortality in patients with prostate cancer have yielded inconclusive findings. This meta-analysis aimed to evaluate the association between overweight/obesity determined by body mass index (BMI) and overall survival (OS) in patients with metastatic prostate cancer (mPC).</p> Methods <p>A systematic search was conducted in the PubMed, Web of Science, and Embase databases until February 2025. Studies that evaluated the association between overweight/obesity and OS in patients with mPC were considered.</p> Results <p>Fifteen studies reported in 13 articles, including 18,280 patients, were identified. The overall pooled adjusted HR for OS was 0.79 (95% CI 0.73–0.85) for patients with overweight/obesity versus those with normal weight. The pooled adjusted HR for OS was 0.81(95%CI 0.75–0.87) for overweight and 0.78 (95%CI 0.67–0.90) for obesity. Furthermore, the association of overweight (HR 0.78; 95% CI 0.71–0.85) and obesity (HR 0.73; 95% CI 0.59–0.90) with OS was more pronounced in patients with metastatic castration-resistant prostate cancer (mCRPC). Additionally, each 1-unit increase in BMI was associated with a 4% (95% CI 1.0–8.0%) improvement in OS.</p> Conclusion <p>Patients with mPC who have overweight or obesity, as defined by BMI, are associated with improved overall survival, particularly in those with mCRPC.</p>