An increasing number of girls are entering the juvenile justice system. However, intervention programs for delinquent girls have not been examined empirically. We examined the 12-month outcomes of a randomized intervention trial for girls with chronic delinquency (N = 81). Girls were randomly assigned into an experimental condition (Multidimensional Treatment Foster Care [MTFC]) or a control condition (group care [GC]). ANCOVAs indicated that MTFC youth had a significantly greater reduction in the number of days spent in locked settings and in caregiver-reported delinquency, and had 42% fewer criminal referrals than GC youth (a trend) at the 12-month follow-up. Implications for reducing girls’ chronic delinquency are discussed.