Androgen deprivation therapy (ADT) leads to important changes in body composition. No data are currently available about the relationship between these treatment-related changes and patient outcome. Using dual-energy X-ray absorptiometry, bone mineral density (BMD), fat body mass (FBM), and lean body mass (LBM) were determined at baseline, and after 1 and 2 years in 53 non-metastatic prostate cancer (PC) patients with high-risk disease treated with adjuvant ADT. Changes in these parameters were correlated with patient outcome in terms of adverse skeletal events, disease recurrence, and overall survival. ADT led to a significant decrease in BMD (p < 0.03) and LBM (p < 0.03), and an increase in FBM, (p < 0.0001). Changes in BMD failed to show any relationship with time to skeletal-related events (SRE), disease recurrence, and death. FBM increase was a significant predictor of higher risk of SRE [hazard ratio (HR) 3.024, 95 % CI 1.004-10.353, p < 0.02], higher risk of death (HR 2.373, 95 % CI 1.012-5.567, p = 0.04), and a non-significant higher risk of disease recurrence (HR 2.219, 95 % CI 0.956-5.150, p = 0.13). LBM decrease did not correlate with either time to SRE or survival, while a non-significant association with disease recurrence (HR 1.550, 95 % CI 0.670-3.605, p = 0.06) was observed. The early increase in FBM may provide predictive information of poor outcome in PC patients given ADT. These data suggest that the adoption of early preventive measures aiming to reduce fat increase can potentially reduce the morbidity and mortality risk.