['We determined whether the ratio of serum testosterone to prostate specific antigen might provide diagnostic value regarding the risk of prostate cancer in a population of hypogonadal men undergoing prostate biopsy.', 'The study population consisted of 184 consecutive men with symptomatic hypogonadism and prostate specific antigen 4.0 ng/ml or less who underwent prostate biopsy before the anticipated initiation of testosterone therapy. All men had testosterone 300 ng/dl or less. Testosterone concentrations were converted to ng/ml, eg 270 ng/dl equals 2.7 ng/ml, to calculate the testosterone-to-prostate specific antigen ratio.', 'Mean patient age was 58.5 years. There were 154 men with benign biopsies and 30 with cancer. Testosterone concentrations were similar in the prostate cancer and noncancer groups, although mean prostate specific antigen was higher in the prostate cancer group. The testosterone-to-prostate specific antigen ratio was inversely related to prostate cancer risk (OR 0.49, 95% CI 0.33-0.74). On multivariate analysis performed by logistic regression neither age nor prostate specific antigen was be predictive of prostate cancer. However, the testosterone-to-prostate specific antigen ratio remained strongly associated with prostate cancer risk. An ROC for the testosterone-to-prostate specific antigen ratio suggested that a ratio of below 1.8 was diagnostic for prostate cancer, while values below this threshold were associated with an OR of 3.17 (95% CI 1.17-8.59) for prostate cancer.'] Does the ratio of serum testosterone-to-prostate specific antigen predict prostate cancer in hypogonadal men?