BACKGROUND: Some strength athletes use androgenic-anabolic steroids (AAS) to improve body dimensions, though the drugs' long- and short-term effects have not been definitively established. OBJECTIVE: This study sought to investigate the short- and long-term effects of AAS self-administration on body dimensions and total and regional body composition. DESIGN: This prospective, unblinded study involved 35 experienced male strength athletes: 19 AAS users (drugs were self-administered) and 16 nonuser controls engaged in their usual training regimens. At baseline, 8 weeks, and 6 weeks after AAS withdrawal (for AAS users) circumferences were measured at 10 sites, and skinfolds measured at 8 sites. To assess differences in AAS regimens, 9 subjects took AAS far 8 weeks (short-AAS) and 10 athletes took AAS for 12 to 16 weeks (long-AAS). Body composition and anthropometry were assessed at baseline, at the end of AAS use, and 6 weeks later. Lean body mass (LBM) was calculated from body weight and percentage fat. Total and regional body composition was measured by dual-energy x-ray absorptiometry. RESULTS: AAS use increased users' body weight by 4.4 kg and LBM by 4.5 kg, and produced increases in several circumferences. Percentage of fat decreased (17.0% to 16.0%), but fat mass remained unchanged. changes persisted 6 weeks after drug withdrawal but were not less than those taken at 8 weeks. Bone-free lean mass of all regional body parts increased in subjects taking AAS, but fat mass was unaffected. Short- and long-term AAS users did not differ in any parameter measured at 8 weeks or after drug withdrawal. CONCLUSION: In AAS users, 8 weeks of self-administered AAS increased body weight, lean body mass, and limb circumferences, but decreased percentage fat compared with controls,Changes remained 6 weeks after drug withdrawal, though for some measurements only partially. AAS stimulated the bone-free lean mass of all body parts, but it did not affect fat mass. Short-term and long-term AAS administration produced comparable effects.