Children in child welfare are especially likely to have unmet mental health needs. The role of family factors in children's use of mental health services was examined in a longitudinal sample of 1,075 maltreated or at-risk children. Vulnerable family environment (poor family functioning, low social support, and caregiver psychological distress) is an important predictor of children's mental health needs. It also predicts them not having these needs met. (Contains 1 table and 1 figure.)