Objective: The objective of this follow-up study was to assess the long-term effects of clinical infant home-visiting services on child outcomes at school entry. Method: Participants were 63 five-year-olds from low-income families, half of whom were referred to parent-infant home-visiting services during the first 18 months of life due to concerns about the caretaking environment. Families received between 0 and 18 months of weekly home visits based on infant age at entry into the study. At age 5, children were rated by teachers on the Preschool Behavior Questionnaire for behavior problems in the classroom and by parents both on the Simmons Behavior Checklist for behavior problems at home and on the Achenbach Social Competence ltems for positive play behaviors with friends. Results: With initial family risk status and child gender controlled, teacher-rated hostile behavior problems decreased in dose-response relation to the duration of early home-visiting services, which accounted for 15% of the variance in child hostile behavior. Parents' reports of positive play behaviors were positively linearly related to service duration. Parents' reports of behavior problems were less reliably related to service duration than teacher reports. Conclusions: Early home-visiting services reduced the incidence of aggressive behavior problems among socially at-risk children for up to 3.5 years after the end of services. J. Am. Acad. Child Adolesc. Psychiatry, 2004;43(6):699-707. Key Words: aggression, intervention, preschool, conduct disorder, oppositional disorder.