To compare demographic, clinical, and familial characteristics across bipolar disorder (BD) subtypes in adolescents. A total of 168 participants, 13 to 19 years of age, with BD-I ( = 41), BD-II ( = 68), or operationalized BD-not otherwise specified (NOS) ( = 59) were recruited from a tertiary subspecialty clinic at an academic health sciences center. Diagnoses were determined using the semistructured K-SADS-PL (Schedule for Affective Disorders and Schizophrenia for School-Age Children-Present and Lifetime Version) interview. Omnibus analyses were followed up with pairwise comparisons. After controlling for age, race, and living with both natural parents, BD-I was associated with greater functional impairment, increased rates of psychiatric hospitalization, psychosis, and lifetime exposure to second-generation antipsychotics and lithium, less self-injurious behavior, less anxiety disorders, and less severe worst lifetime depression and lower levels of emotional dysregulation and lability compared with both BD-II and BD-NOS. Lifetime most severe manic symptoms were highest in BD-I, lowest in BD-NOS, with BD-II intermediate. Lifetime exposure to psychosocial treatment followed the opposite pattern: lowest in BD-I, highest in BD-NOS, with BD-II intermediate. Variables for which there were no significant between-group differences included suicidal ideation, suicide attempts, comorbidities other than anxiety, or family history of BD. Among observed differences, most distinguish BD-I from other subtypes, whereas few variables differed between BD-II and BD-NOS. Different BD subtypes share important similarities in multiple clinical and familial characteristics, including family history of BD. Present findings support and extend knowledge regarding the course and outcome of bipolar youth study operationalized definition of BD-NOS. Further research is warranted to evaluate intermediate phenotypes and treatment strategies that address these subtype-related differences.