To examine the effects of quantity of nonmaternal care across the first 3 and 5 years of life on problem behavior and affective-cognitive indices of adjustment, and to test the hypotheses that parenting mediates effects of nonmaternal care, 120 working- and middle-class, two-parent Caucasian families rearing firstborn sons were studied. More time in nonmaternal care across the first 3 and 5 years predicted more mother-reported externalizing problems when children were ages 3 and 5 (and somewhat more father-reported externalizing problems at age 5), as well as more negative mothering and less positive fathering during the toddler years. Effects of nonmaternal care on externalizing problems became insignificant once observed parenting was controlled, thereby providing evidence of the mediational effects of parenting. More time in nonmaternal care across the first 5 years predicted more negative adjustment on a composite lab-based measure of affective-cognitive functioning at age 5 (e.g., attributional bias, social problem solving, preference for negative story plots), and this effect was only modestly attenuated upon controlling for parenting. Results are discussed in terms of related research and the current context of child care in America.