Pediatric-onset bipolar disorder is common but often difficult to diagnose in younger patients. Clinicians should be sure to establish the presence of a full manic episode to make the diagnosis of bipolar I disorder. Because adult criteria are used for children and adolescents, clinicians also should be aware of developmental norms that can help to make an accurate diagnosis. Bipolar disorder NOS and other disorders in children and adolescents may be prodromal states for bipolar disorder, especially in the presence of a positive family history.