ABSTRACT A common belief among professionals and researchers involved with the rehabilitation of juvenile delinquents is that residential treatment for these youngsters reinforces rather than inhibits their patterns of delinquent behaviors. The present study included the entire Jewish male population referred by the Israeli juvenile court to residential treatment during a period of six years (1969 to 1975). During this period, 2050 juveniles were sentenced to residential treatment. Their criminal records before, during, and after incarceration up to three years were checked. Due to errors in I.D. numbers, criminal records of only 1331 (64.93%) were retrieved. Mean age at first confinement of the inmates was 13.45 (S.D. = 2.3) years. Average length of stay in institutions ranged from one month to more than eight years with mean of 19.7 months (S.D. = 16.6 months). Since juvenile delinquents referred to community based, non-residential, treatment programs cannot serve as a control group due to different treatment needs and methods, no controls were assessed. However, the study included subjects who were placed in all available residential treatment facilities in Israel and evaluated them by the same measurements. The study provides a comprehensive analyses of residential treatment and an empirical base for comparison of different types of institutions. Findings clearly indicate that, at least in Israel, incarceration in a residential treatment facility did not increase the level of delinquency of the inmates.