The aim of this study was to examine the relationship between externalizing behaviors and the quality of attachment representations in preschool children, and to determine if family type and custody arrangement had a moderating effect on this relationship. The participants were 33 girls and 31 boys (n = 64) aged between three and six years (M = 4.75; SD = 0.87 years) and their mothers. Among them, 36 came from “intact” families, 13 were living mainly with their mothers and 15 were in joint physical custody. Children’s attachment representations were assessed with the Attachment Story Completion Task (Bretherton, Ridgeway & Cassidy, 1990). Mothers reported on their child’s behavior problems using the Child Behavior Checklist (Achenbach & Rescorla, 2001) and on their alliance with the father using the Parenting Alliance Inventory (Abidin & Brunner, 1995). Although children’s externalizing behaviors were found to be associated with the disorganization of their attachment representations, this relationship was significantly weaker and was non‐significant for children in joint physical custody. Thus, the results of this pilot study suggest that joint custody may protect children of separated parents from the effects of attachment disorganization on externalizing behaviors.