This study used data from 75 adolescent mothers to examine relations among adolescent mothers' attachment avoidance and anxiety, their ability to trust their child's father, and their perceptions of the quality of their coparenting relationship with their child's father. Results suggest that mothers with lower avoidance had more trust for their child's father and also had coparenting relationships characterized by less conflict and a stronger parenting alliance. Moreover, trust mediated the associations between mother's avoidance and coparenting quality. In contrast, mothers' attachment anxiety was not associated with trust for their child's father or their perceptions of coparenting relationship quality. This study provides evidence that adolescent mothers' relationship histories may play an important role in the quality of the coparenting relationship they have with their child's father. (Contains 2 tables.)