New estimates for the risk of becoming stimulant dependent within 24 months after first extra-medical (EM) use of a stimulant drug compound are presented, with a focus on subgroup variations in this risk (e.g., alcohol dependence, male-female differences). The study estimates are derived from a representative sample of United States residents ages 12 and older (n=166,737) obtained from the 2003 to 2005 National Surveys on Drug Use and Health. A total of 1700 respondents were found to have used stimulants extra-medically for the first time within 24 months prior to assessment. Approximately 5% of these recent-onset EM users had become stimulant dependent since onset of EM use. As hypothesized, alcohol dependence cases were found to have experienced an excess risk of becoming stimulant dependent soon after onset of stimulant drug use; there was no robust male-female difference in risk. Independently, initiates who had used multiple types of stimulants extra-medically, and methamphetamine users, were more likely to have become stimulant dependent soon after onset of use; by comparison, EM users of methylphenidate (Ritalin) were less likely to have developed rapid-onset dependence. These epidemiologic findings help quantify a continuing public health burden associated with new onsets of extra-medical stimulant use in the 21st century.