This review addresses the phenomenology of mania/bipolar disorder from a developmental psychopathology perspective and uses cases with longitudinal information to illustrate major points. Beginning with a summary of the phenomenology of bipolar illness as it occurs in adults, the authors identify diagnostic complexities unique to children and adolescents. These include the challenges of characterizing elation and grandiosity; differentiating mania from comorbid symptoms, rages, sequelae of maltreatment, and typical developmental phenomena; and the unique manifestations of psychosis. We conclude with the observation that a significant difference between early and later onset bipolar disorder is that, in the former, there appears to be a global delay or arrest in the development of appropriate affect regulation; whereas in adult-onset bipolar illness, emotion dysregulation generally presents as an intermittent phenomenon. At this juncture, the study of childhood bipolar illness would benefit from a developmental psychopathology perspective to move beyond the level of cross-sectional symptom description to begin to study individuals over time, focusing on developmental, environmental, genetic, and neurobiological influences on manifest behavior.