The association between early parent-child attachment security and peer rejection among preschool children was examined. Children in three preschool classrooms (N = 37) participated. Mothers rated their children's attachment security at age 3 years on the Attachment Q-Set (Waters, 1987). Sociometric ratings were collected from classmates at age 4 years through individual picture interviews. Teachers rated externalizing and internalizing behaviour exhibited at preschool. Lower attachment security was associated with greater subsequent peer rejection and higher externalizing and internalizing behaviour scores. An exploratory path model suggested that the linkage between early insecure attachment and later peer rejection may be mediated by externalizing behaviour.