Numerous national surveys and surveillance programs have shown a substantial rise in the abuse of prescription opioids over the past 15 years. Accessibility of these drugs to non-patients is the result of their unlawful channeling from legal sources to the illicit marketplace (diversion). Empirical data on diversion remain absent from the literature. This paper examines abusers' sources of diverted drugs from two large studies: 1) a national sample of opioid treatment clients (N=1983), and 2) a South Florida study targeting diverse populations of opioid abusers (N=782). The most common sources of diverted medications were dealers, sharing/trading, legitimate medical practice (e.g., unknowing medical providers), illegitimate medical practice (e.g., pill mills), and theft, in that order. Sources varied by users' age, gender, ethnicity, risk-aversiveness, primary opioid of abuse, injection drug use, physical health, drug dependence, and either access to health insurance or relative financial wealth. Implications for prescription drug control policy are discussed.