This study examined whether infant attachment security moderates the association between parenting in preschool and later aggressive behavior among a sample of children at high risk for developing conduct problems. Participants were 82 adolescent mother-child dyads recruited from the community. Infant attachment status at age 1 year was measured using the Strange Situation. When children were aged 4.5 years, mothers reported on their self-efficacy in regards to parenting, and mothers' positive parenting and criticism were coded from direct observations of parent-child interactions. In grade 1, mothers reported on their children's aggressive behavior. Infant secure attachment significantly moderated the association between observed maternal criticism and child aggression. That is, among insecurely attached children, higher levels of maternal criticism were associated with more severe aggression. This longitudinal finding suggests that a secure attachment may buffer the deleterious effects of harsh parenting on child aggression.