Juvenile reoffending is a costly and perplexing social problem. However, research and theory concerning juvenile reoffending have neglected to examine how young men's gender identities are constructed in the context of a juvenile justice system in which behavior reform through various therapies is a primary goal. This study draws on observational fieldwork in two residential correctional facilities and interviews with incarcerated juvenile male offenders to understand how masculinities are shaped within these institutional settings. They find that in the two settings, hegemonic forms of masculinities involving competition, hierarchy, stoicism, sexism, and homo-phobia were reinforced through institutional and interpersonal mechanisms. While alternative gender identity expressions were offered through various therapies, they were largely suppressed. This illustration of how masculinities are constructed in juvenile corrections provides a new way to examine the inner workings of institutions that are geared to change the attitudes and behaviors of the young men whom they serve.