Sarcopenia is a common skeletal muscle disorder in older people. Here we explore the prevalence of sarcopenia and its impact on men with prostate cancer. We searched PubMed, Embase, and Web of Science databases for relevant studies with an explicit definition of sarcopenia in men with prostate cancer which were published between years 2000 and 2022. Prevalence of sarcopenia and its association with time to biochemical recurrence (BCR), progression-free survival (PFS), non-cancer mortality, overall survival (OS), and treatment-related complications in men with prostate cancer were explored. The summary prevalence, hazard ratios (HRs), and 95% confidence intervals (CIs) were calculated. A total of 24 studies comprising 3,616 patients with early and advanced prostate cancer were included. The prevalence of sarcopenia and sarcopenic obesity was 43.8% (95% CI 19.2%–68.5%) and 24.0% (95% CI 5.0%–43.1%), respectively. Sarcopenia was not associated with a shorter time to BCR (HR 0.89, 95% CI 0.64–1.23, p = 0.48), a shorter PFS (HR 1.20, 95% CI 0.73–1.97, p = 0.48), or a shorter OS (HR 1.29, 95% CI 0.90–1.85, p = 0.16). In contrast, sarcopenia was significantly associated with a higher non-cancer mortality (HR 1.85, 95% CI 1.23–2.80, p = 0.003). In four out of five studies eligible for assessment, sarcopenia was not associated with an increased risk of treatment-related complications. Sarcopenia increases the risk of death from other causes in men with prostate cancer. Patients with prostate cancer should be assessed and managed for sarcopenia in everyday clinical practice.