The Treatment Episode Data Set was examined for trends in the number of adolescents admitted to substance abuse treatment centers and for changes in the routes of heroin administration. Thirteen adolescents in one treatment program who used heroin were compared with 536 adolescents who did not use heroin. Between 1992 and 1996, heroin-using youths represented 2.0 percent of youths in treatment; in 1997 they represented 2.6 percent. Heroin-using youths represented 56 percent of those using injection drugs. Heroin-using youths from one treatment program had significantly more poly-substance dependence compared with adolescents who did not use heroin. Nationally there has been an increasing number, but not percentage, of heroin-using youths in treatment between 1992 and 1996. In 1997 there was an increase in both the number and percentage of heroin-using youths in treatment. Heroin-using adolescents had the highest rate of injection drug use when compared with youths using other substances. Because of their greater risk of contracting human immunodeficiency virus through injection drug use, treatment trials for these adolescents are needed. 4 tables, 1 figure, and 25 references