Although hormones play fundamental roles in prostate growth, their clinical significance is not completely clear. Aims of present study were to assess whether testosterone and serum sex hormone levels are predictors of benign prostatic hyperplasia (BPH) or prostate cancer (PC) and to verify whether prostate cancer is associated with low testosterone levels, and to test association between testosterone levels and known prognostic factors in prostate cancer. In 206 consecutive patients with benign prostatic hyperplasia or prostate cancer testosterone, follicle-stimulating hormone, luteinizing hormone and prolactin levels were tested and correlated with disease. In patients with prostate cancer, hormone levels were also correlated with known prognostic factors. Predictive value was assessed for age, prostate-specific antigen (PSA), PSA ratio, PSA density, prostate volume and serum sex hormone levels using multiple logistic regression analysis and receiver operating characteristic curves. Considering sex hormones, only testosterone levels were significantly lower in patients with prostate cancer than those with BPH; testosterone levels appear to be independent predictor of prostate cancer, enhancing predictive accuracy for BPH and PC. Testosterone levels do not seem to be associated with known clinical prognostic factors. This study supports experimental findings that testosterone levels are predictor of prostate cancer and that prostate cancer is frequently associated with low testosterone levels. In the diagnostic work-up for prostate cancer, adding testosterone determination to PSA test may improve predictive accuracy.