Despite the fact that sports organizations and legislators have introduced various mechanisms to discourage athletes from using performance and appearance enhancing substances a high percentage of athletes admits to their unabated application. In competitive athletics, bodybuilding and in recreational sports anabolic androgenic steroids (AAS) continue to be the substances most abused. This review summarizes the side effects of AAS abuse on organs and system functions in both sexes. High doses of AAS cause a significant increase of erythrocytes and hemoglobin concentration, which may lead to thromboembolism, intracardiac thrombosis and stroke. Long-term AAS abusers have a higher incidence of arrhythmias, atherosclerosis, concentric left-ventricular myocardial hypertrophy with impaired diastolic function and also sudden cardiac death. Changes of liver function and structure, up to hepatocellular carcinoma, have been described, mainly in cases of chronic misuse of 17α-alkylated AAS. Sleeplessness, increased irritability, depressive mood status are often observed in AAS abuse. In former AAS abusers depression, anxiety and melancholy may persist for many years. Due to negative feedback in the regulation of the hypothalamic-pituitary-gonadal axis AAS can cause reversible suppression of spermatogenesis up to azoospermia. In women the changes most often caused by AAS abuse are hirsutism, irreversible deepening of voice, dysmenorrhea, secondary amenorrhea with anovulation and infertility. AAS abuse notwithstanding, under clinical conditions testosterone remains the most important hormone for substitution therapy of male hypogonadism.