Anabolic-androgenic steroids (AAS) are synthetic derivatives of testosterone. Testosterone was isolated in the early 20th century. For the past 50 years anabolic steroids have been at the forefront of the controversy surrounding performance enhance drugs. According to surveys and media reports, the legal and illegal use of these drugs is gaining popularity. Testosterone has potent anabolic effects on the musculoskeletal system, including an increase in lean body mass, a dose-related hypertrophy of muscle fibers, and an increase in muscle strength. In addition, testosterone and its synthetic derivatives are resposible for the development and maturation of male secondary sexual characteristics (i.e. increase in body hair, masculine voice, development of male pattern baldness, libido, sperm production and aggressiveness). Side-effects of anabolic steroids include cardiomyopathy, atherosclerosis, hypercoagulopathy, elevated blood pressure, myocardial hypertrophy, arrhythmia, thrombosis, dermatologic disorders, libido changes, subfertility, testicular atrophy, impotence, hepatic dysfunction, and psychiatric and behavioural disturbances. For athletes requiring speed and strength and men desiring a cosmetic muscle makeover, illegal steroids are a powerful lure, despite the risk of subjective side effects. Recent clinical studies have discovered novel therapeutic uses for physiologic doses of AAS, without any significant adverse effects in the short term. In the wake of important scientific advances during the past decade, the positive and negative effects of AAS warrant reevaluation.