Parental history suggests that nonepisodic irritability and hyperarousal, or “severe mood dysregulation, ” in children is not a form of bipolar disorder. Bipolar illness has a strong genetic component, and an onset during childhood is associated with a particularly strong family history. However, Brotman et al. (p. 1238) discovered that parents of children with severe mood dysregulation were much less likely to have a diagnosis of bipolar disorder, compared to parents of children with strictly defined bipolar disorder. Dr. Gabrielle Carlson discusses these findings in an editorial on p. 1140. Looking below the diagnostic level, Potash et al. (p. 1229) catalogued clinical features of bipolar disorder in two large family studies. The resulting Bipolar Disorder Phenome Database includes 5,721 subjects and allows identification of specific clinical subtypes, which may be more genetically homogeneous than the overall diagnosis. Researchers can now explore connections between clinical variables and genetics with adequate numbers of subjects to detect even moderate genetic effects.