Research examining the demographic and substance use characteristics of illicit drug use in the United States has typically failed to consider differences in routes of administration or has exclusively focused on a single route of administration?injection drug use. Data from National Survey on Drug Use and Health were used to compare past-year injection drug users and non-injection drug users' routes of administration of those who use the three drugs most commonly injected in the United States: heroin, methamphetamine, and cocaine. Injection drug users were more likely than those using drugs via other routes to be older (aged 35 and older), unemployed, possess less than a high school education, and reside in rural areas. IDUs also exhibited higher rates of abuse/dependence, perceived need for substance abuse treatment, and co-occurring physical and psychological problems. Fewer differences between IDUs and non-IDUs were observed for heroin users compared with methamphetamine or cocaine users.