Transdermal testosterone gels represent an effective alternative to injectable testosterone preparations. Short-term (6 months) data demonstrated positive effects on muscle, bone, fat, libido and mood. This report provides a preliminary analysis of longer-term treatment with a testosterone gel (AndroGel or Testogel) in a group of men aged 19-67 years of age. The positive effects of testosterone treatment on all of the above parameters persisted in this 3-year follow-up. The benefits occurred independent of age (equally in the older and younger subjects). The positive effects of transdermal testosterone gel on bone mineral density previously identified at 6 months of treatment, continued with time. The positive effects on bone mineral density were greater in the spine than the hip. There were minimal effects on lipid levels. Levels of prostate-specific antigen (PSA) increased with testosterone treatment but, in general, remained in the normal range. Three subjects (1.8%) were shown to have elevated PSA and biopsy-proven prostate cancer. It was not possible to determine if this incidence is above the background rate. Monitoring for prostate disease through PSA measurements and digital rectal examination is recommended for hypogonadal men in the older age groups when treated with testosterone.