Objective: To determine whether positive parenting practices are associated with less aggressive and delinquent behavior in early-maturing girls. Design: Cross-sectional survey. Setting: Interviews with a community sample of children and their caregivers were conducted in their homes or in a research setting. Participants: An ethnically diverse cohort of 330 fifth-grade girls (mean age, 11.25 years) from 3 metropolitan areas. Main Exposure: Early onset of menarche, parental nurturance, knowledge of the child's activities, and communication. Main Outcome Measures: Physical, relational, and nonphysical aggression and delinquent behavior. Results: A total of 25% of girls could be reliably classified as early maturers. Early maturation was associated with delinquency (b = 0.53) but not aggression. Low levels of maternal nurturance were associated with delinquency and relational aggression (both b = -0.04). Early maturation was associated with higher relational aggression only at low levels of nurturance (b = 0.94), communication (b = 1.36), and knowledge (b = 1.06) (P < .05 for each interaction). Also, early maturation only predicted physical aggression when combined with low maternal nurturance (b = 0.93). Conclusions: Early puberty is a risk factor for delinquency, and early puberty combined with low parental nurturance, communication, or parental knowledge of the child's activities presents a risk for aggressive behavior in early adolescent girls. Early-maturing girls may benefit from increased parental nurturance, communication, and knowledge. ©2008 American Medical Association. All rights reserved.