Fifty-one human immunodeficiency virus-positive men with hypogonadism and wasting were randomized to receive testosterone enanthate, 300 mg im every 3 weeks, or placebo for 6 months, followed by open-label testosterone administration for 6 months. Subjects initially randomized to placebo gained lean body mass (LBM) only after crossover to testosterone administration (mean change ± standard error of the mean, −0.6 ± 0.7 kg [months 0–6] vs. 1.9 ± 0.7 kg [months 6–12]; P = .03). In contrast, subjects initially randomized to testosterone continued to gain LBM during open-label administration (2.0 ± 0.7 kg [months 0–6] vs. 1.6 ± 0.6 kg [months 6–12]; P = .62) and had gained more LBM at 1 year than did subjects receiving testosterone for only the final 6 months of the study (3.7 ± 0.8 kg vs. 1.0 ± 1.0 kg; P = .05). Testosterone administration results in sustained increases in LBM during 1 year of therapy in hypogonadal men with AIDS wasting.