Evidence from 2 longitudinal studies of infant and family development was combined and examined in order to determine if experience of extensive nonmaternal care in the first year is associated with heightened risk of insecure infant-mother attachment and, in the case of sons, insecure infant-father attachment. Analysis of data obtained during Strange Situation assessments conducted when infants were 12 and 13 months of age revealed that infants exposed to 20 or more hours of care per week displayed more avoidance of mother on reunion and were more likely to be classified as insecurely attached to her than infants with less than 20 hours of care per week. Sons whose mothers were employed on a full-time basis (greater than 35 hours per week) were more likely to be classified as insecure in their attachments to their fathers than all other boys, and, as a result, sons with 20 or more hours of nonmaternal care per week were more likely to be insecurely attached to both parents and less likely to be securely attached to both parents than other boys. A secondary analysis of infants with extensive care experience who did and did not develop insecure attachment relationships with their mothers highlights several conditions under which the risk of insecurity is elevated or reduced. Both sets of findings are considered in terms of other research and the context in which infant day-care is currently experienced in the United States.