Objective: To investigate the effects of mesterolone on prostate in patients treated for aging male syndrome. Methods: The cross-sectional study was conducted from June to September, 2009, at endocrinology and metabolism department of Yuzuncu Yil University, Van, Turkey, and comprised patients with symptoms of aging male syndrome and/or low testosterone. They were given mesterolone 50mg/day per oral for two months. Aging Male Symptoms and International Prostate Symptom Score questionaires and prostate-related quality of life scores were completed and prostate ultrasonography (USG) was performed before and after the treatment. Total testosterone, free testosterone, gonadotropins, estradiol, prolactin, sex-hormone binding globulin, as well as total and free prostate-specific antigen were also studied. Results: Of the 34 patients in the study, 22(64.70%) had their prostate volume increased, while 12(35.29%) had it decreased. The change, however, was not statistically significant (p<0.098). Mesterolone significantly improved Aging Male Symptoms, International Prostate Symptom and prostate-related quality of life scores (p<0.001). These improvements though significant were independent of the changes in prostate volume. Total testosterone, sex-hormone binding globulin andestradiol decreased, while free testosterone showed no change (p<0.002, p<0.001, p<0.024, p<0.337). The fraction of free testosterone increased (p<0.001), while total and free prostate-specific antigen did not change (p<0.368 and p<0.841) Conclusion: Mesterolone proved to be a safe alternative in the treatment of Aging Male Syndrome. It also improved lower urinary tract symptoms and prostate-related quality of life.