Most treatment studies of opioid-dependent populations have focused predominantly on heroin users, despite a recent increase in those dependent upon prescription opioids. A key methodological challenge involved in studying the latter group involves defining the population. Specifically, researchers must decide whether to include (1) concurrent heroin users and (2) individuals with pain. The multi-site Prescription Opioid Addiction Treatment Study is examining treatments for this population. This paper describes various inclusion criteria considered by the study team related to heroin use and pain. The goal was to recruit a distinct but generalizable population of individuals dependent upon prescription opioids. (Am J Addict 2010;00:1-6).