In this issue of the Journal, two articles (1, 2) provide a rare developmental prospective on the brain processes involved in cognition and emotion in bipolar disorder. It is well established that bipolar disorder can have childhood onset. Indeed, retrospective studies have found that adult patients report childhood onset in the majority of cases (3). Furthermore, childhood onset is associated with greater severity of illness (3). The two studies in this issue are among the first to simultaneously study both youths and adults with bipolar disorder using the same diagnostic techniques and imaging methods. Both studies were supported by the National Institute of Mental Health intramural research program, in which there has been an emphasis on the importance of identifying the “narrow phenotype” of bipolar disorder (4). The pediatric patients in these two studies had a history of at least one hypomanic or manic episode with elevated mood or grandiosity as well as key DSM-IV-TR criterion B symptoms for mania. Thus, neither study included children with mood dysregulation, i.e., patients with chronic irritability/aggression who are often diagnosed with bipolar disorder not otherwise specified in clinical settings. The participants in these studies differed in comorbidity. Weathers et al. (1) excluded individuals with attention deficit hyperactivity disorder (ADHD), while two-thirds of the children and 12% of the adults in the Kim et al. study (2) did meet criteria for ADHD. It was appropriate to exclude individuals with ADHD from the Weathers et al. study because inhibitory control was being assessed, and thus high comorbidity with ADHD would have been a confound. The mean age at mania onset in the pediatric samples ranged from about 9 to 11 years, while the mean age at mania onset in the adult samples was about 21 years. Thus, the pediatric patients (mean age, 14 years) had been ill for about 3–5 years, while the adult patients (mean age, 40 years) had been ill for two decades.