To better understand the distinguishing characteristics of methamphetamine users versus cocaine users, we conducted a retrospective chart review of the 345 patients admitted to an outpatient stimulant treatment program during 1995--1997. Analyses revealed an increase in methamphetamine patients over the 3-year period, and that these patients were more likely than cocaine patients to be male, Caucasian, and gay or bisexual. Methamphetamine patients were also more likely to be HIV-positive, engage in behaviors such as using and sharing needles that place them at high risk for HIV transmission, have a psychiatric diagnosis, and be on psychiatric medications. The two populations did not differ in treatment adherence, as measured by clinic attendance, drug-free urines, and successful completion of treatment. These findings suggest that highly specialized substance abuse treatments for methamphetamine patients may not be needed. Resources may be directed toward addressing their medical and psychiatric diagnostic issues by providing ancillary services to stimulant treatment programs.