Recently there has been increasing interest in the role that emotionality plays in children's social functioning. In this paper, we examined changes in preschoolers' tendencies to play alone as a function of their dispositional negative emotional intensity (DNEI). Additionally, we examined changes in expressed negative emotion. The solitary play and expressed negative emotions of 94 children (mean age = 50.5 months) were observed for 3 months. Teachers completed a measure of DNEI. Growth curves revealed that children high in DNEI evidenced increasing rates of solitary play and decreasing rates of expression of negative emotions. Children high in DNEI were initially higher in observed emotional intensity. Findings suggest that children who have difficulty regulating negative emotions increasingly become isolated from peers.