Relations between nonmaternal child care and ratings of maternal sensitivity and child positive engagement during mother-child interaction at 6, 15, 24, and 36 months were examined for 1,274 mothers and their children participating in the National Institute of Child Health and Human Development (NICHD) Study of Early Child Care. In longitudinal analyses that controlled for selection, child, and family predictors, child care was a small but significant predictor of maternal sensitivity and child engagement. For the whole sample, including families who did and did not use child care, more hours of child care predicted less maternal sensitivity and less positive child engagement. For children who were observed in child care, higher quality child care predicted greater maternal sensitivity, and more child-care hours predicted less child engagement. The effects of child care on mother-child interaction were much smaller in the analytical models than the effects of maternal education but were similar in size to the effects of maternal depression and child difficult temperament. Patterns of association with child care did not differ significantly across ages of assessment.