AAS use is one of the few types of substance use where a diagnosis is often suggested simply by looking at the patient as he walks through the door (Pope and Kanayama 2005). As we have described elsewhere (Kouri et al. 1995), there is a fairly sharp upper limit of muscularity that can be achieved by a lean individual without the help of drugs. We have published a formula to calculate muscularity, expressed as the fat-free mass index (FFMI), which clinicians can apply if they know the height, weight, and approximate percentage of body fat of the patient (Kouri et al. 1995). Men who have low body fat and display an FFMI of greater than approximately 26 kg/m² are almost certainly using drugs that help them to achieve their size. We have published photographs comparing bodybuilders who have used AAS with those who have not to aid the clinician in making this distinction (Pope and Brower 2004). Clinicians who suspect AAS use in any patient should follow several guidelines, described in the following section, to take a specific history.