Mothers' perceptions of marital quality and depressed mood and children's attachment security and friendship quality were assessed in the National Institute of Child Health and Human Development Study of Early Child Care and Youth Development. One month after their birth and again when the children were 3 and 4 years old and in first and third grades, mothers rated the quality of their marital relationship; when the children were 2 years old, the Attachment Q-Set was used to assess the mother-child attachment relationship; the Center for Epidemiologic Studies Depression Scale was used to measure the mother's depressed mood when the child was 2 years old and in third grade; and when children were in fourth grade, they were observed interacting with their best friend to assess friendship quality. Using a series of regression and path analyses, we determined whether and how marital quality, maternal mood, and attachment security predicted friendship quality. Better quality friendship interactions in fourth grade were significantly associated with better marital quality and greater attachment security. The association between marital quality and friendship quality was partially mediated by attachment security. Friendship quality was not related to maternal mood.