OBJECTIVE To determine the prevalence of occult prostate cancer in men with low serum total testosterone or free testosterone levels. METHODS Retrospective analysis of a consecutive series of men. METHODS Academic teaching hospital. METHODS Seventy-seven men with low total testosterone or free testosterone levels, with normal results of digital rectal examination and prostate-specific antigen (PSA) levels of 4.0 ng/mL or less. The mean age was 58 years. METHODS Sextant prostate needle biopsies with ultrasound guidance. METHODS Results of prostate needle biopsies, transrectal ultrasound, prostate volume, PSA level, PSA density, total and free testosterone levels. RESULTS Prostate cancer was identified in 14% (11/77) of the entire group and in 10 men (29%) aged 60 years or older. The median age for men with cancer was 64 years. Histologic examination showed Gleason scores of 6 or 7 for all cancers. No significant differences were noted between the cancer and benign groups with regard to PSA level, PSA density, prostate volume, total testosterone level, or free testosterone level. CONCLUSIONS A high prevalence of biopsy-detectable prostate cancer was identified in men with low total or free testosterone levels despite normal PSA levels and results of digital rectal examination. These data suggest that (1) digital rectal examination and PSA levels are insensitive indicators of prostate cancer in men with low total or free testosterone levels, and (2) PSA levels may be altered by naturally occurring reductions in serum androgen levels.