Anabolic-androgenic steroids are controlled substances that are taken illicitly to enhance physical appearance and performance. In addition to the desired somatic effects, reasonably good evidence suggests that AASs are capable of influencing mood and behavior. A myriad of adverse effects have been reported. Although many of these effects appear to reverse with cessation of use, fatalities due to suicides, homicides, liver disease, heart attacks, and cancer have been reported infrequently among illicit users. Although studies are needed to quantify more precisely the long-term consequences and risks of using AASs, patterns of illicit use are particularly troublesome. The use of extremely high doses, needles, counterfeit and veterinary drugs, and multiple steroidal and nonsteroidal drugs simultaneously may further enhance the risks of using AASs. The clinician should suspect AAS use in high-risk individuals who manifest any of the possible consequences described in this article. Laboratory tests can be valuable for detection of use and assessment of consequences. Treatment approaches may borrow from proven techniques employed with other substance abusers, but should also address the special value that physical attributes and body image have for the AAS user.