Objective: To examine the association between youth comorbid psychiatric disorders, maternal mood disorder, and perceptions of family cohesion and conflict among youth diagnosed with pediatric bipolar disorder (PBD). Method: Three hundred eighty-nine bipolar youths and their parents completed a diagnostic interview and instruments assessing family psychiatric history and functioning. Family functioning was assessed with the Family Adaptability and Cohesion Scales-II and the Conflict Behavior Questionnaire. Results: The presence of a maternal mood disorder was associated with lower family cohesion. The presence of a youth externalizing disorder with or without a co-occurring anxiety disorder was also associated with lower family cohesion as well as higher family conflict. Furthermore, the negative relationship between maternal mood disorder and family functioning was stronger in the presence of a youth externalizing disorder. Conclusions: Youth comorbidity and maternal mood disorders appear to be associated with worse family functioning among bipolar youths. Family-based treatments with bipolar youths may need to integrate treatment of youth comorbidity and address maternal mood disorder for optimal results. (Contains 4 tables.)