African American youth from single mother homes are at greater risk for internalizing and externalizing problems relative to their peers from two-parent homes. Although the predominance of psychosocial research on these youth has focused on maternal parenting and mother-child relationship quality, far less attention has been devoted to the quality of the relationships that youth have with "nonmarital coparents," or other adults and family members who assist African American single mothers with childrearing. This study examined the contribution of the youth-coparent relationship to psychosocial adjustment among African American youth from single mother families (n = 141). Findings revealed that maternal parenting and youth-coparent relationship quality interacted to predict both youth internalizing and externalizing problems. Specifically, greater youth-coparent relationship quality enhanced the protective role of maternal positive parenting. Findings suggest the potential role of broader familial and social contexts for enhancing the protective effects of positive parenting.