The clinical characteristics and adaptive functioning of preschoolers who met DSM-IV criteria for bipolar disorder versus psychiatric and healthy comparison groups were investigated. A community-based sample of 303 preschoolers (3–6 years of age) and their caregivers was ascertained. Diagnostic classification based on parent report of mania symptoms was made using an age-appropriate psychiatric interview. Results indicated that 26 preschoolers met DSM-IV criteria for bipolar disorder who could be identified based the presence of 13 core age-adjusted mania items. These children could be clearly differentiated from children in two psychiatric groups (DSM-IV disruptive disorders, and major depressive disorder) and a “healthy” comparison group based on a specific symptom constellation. Findings indicated that preschoolers in the bipolar group were significantly more (p < .05) impaired than the two psychiatric and healthy groups based on independent measures. Further, even after controlling for comorbid attention-deficit/hyperactivity disorder (81% comorbidity rate), the bipolar group remained significantly (p < .05) more impaired in multiple domains compared to preschoolers with DSM-IV disruptive disorders and healthy controls. Findings suggested that children as young as 3 years can manifest DSM-IV bipolar disorder when age adjusted symptom descriptions are employed, and that these children can be distinguished from healthy and disruptive disordered preschoolers. Recommendations for future research in this area that integrates developmental and mental health models are made.We gratefully acknowledge Edward Spitznagel for his statistical consultation. We are also grateful to the The Early Emotional Development Program staff, our preschool participants and their parents, and community recruiting sites whose participation and cooperation made this research possible. Funding for the study of preschool depression was provided by NIMH Grant NIMH R01 MH64769-01 (to J.L.).