Although attention has been focused on uncovering the etiology of drug abuse and addiction, no studies have been commissioned to discover the prevalence of heroin use in Ireland. Given the fact that nearly 50 percent of Ireland’s population consists of persons younger than 25, there is a need to discover the prevalence of drug use among young persons and also to examine whether this drug use contributes to the decision to drop out of school. The author examined 3 separate 1996 data sources, hospital admissions, police records, and the methadone treatment list, and collected survey data on 112 students who had left school early but had returned to further their education. The survey questionnaire asked about details concerning their education, including why they left school early, and about perceived and actual drug use. The capture-recapture method was used to generate an estimate of the prevalence of heroin use based on the degree of overlap between two or more samples. Results revealed that at least 1,528 young people in Dublin between the ages of 10 and 20 years had used heroin in 1996. However, using 3 samples, the study estimated that 4,081 young people were using heroin in Dublin in 1996. Using 2 samples, it was estimated that 1,141 of these were problem users in 1997. Furthermore, results indicated that 51.1 percent of those surveyed had used drugs before they left school and 46.5 percent reported that their drug use affected their schooling. The results suggest that drugs do play a part in school drop-out behavior. From a public policy perspective, it is important to conduct more research on drug use and whether drug use influences the decision to leave school early. Targeted early interventions may be designed more appropriately once more information is known about the extent and etiology of the problem in Dublin. Tables, references