The purpose of the study was to examine the differential relations between mother-child reminiscing about a positive emotional event vs. a negative emotional event and attachment security, family climate, and young children's socioemotional development. Fifty preschool children (M age = 50.69 months, SD = 4.64) and their mothers completed two reminiscing conversations at the laboratory, which were coded for emotion-laden discourse, affect, and elaboration, and children completed measures of emotional understanding and representations of relationships. At their homes, mothers completed the attachment Q-sort and the self-report family inventory. Both attachment security and family climate were related to the quality of mother-child affect and maternal elaboration during both positive and negative reminiscing conversations. Attachment security and family climate, however, were principally related to discussion of emotion during the negative event discussions. In addition, it was mother-child reminiscing about the negative emotional event that was associated with high levels of children's socioemotional development.