Although pharmacological treatments can help alleviate mood symptoms in youth with paediatric bipolar disorder (PBD), residual symptoms still commonly persist. In many cases, these symptoms seriously affect the social and psychological development of children and adolescents suffering from PBD. Complementary interventions, such as psychosocial and psychoeducational treatments, can help children and their families manage mood regulation and other challenges throughout childhood and adolescence. However, most research on such interventions has focused on children, single‐family psychoeducation, and individual cognitive behavioural therapy. The present study, conducted in Sweden, used a case‐series design to explore whether child‐ and family‐focused cognitive behavioural therapy (CFF‐CBT) for PBD, adapted from children (8–12 years) to adolescents (13–18 years) and applied in a multi‐family format, could help reduce symptoms, improve psychosocial functioning, increase parents' knowledge of and skills for coping with the disorder, and improve family expressed emotion for adolescents with PBD. Furthermore, we aimed to assess whether the effects of such CFF‐CBT are maintained at a one‐year follow‐up. Seven adolescents and 11 parents in two multi‐family groups received twelve sessions of CFF‐CBT. Self‐rating questionnaires and clinical observations were used to evaluate clinically significant changes for individual cases. The results suggest that CFF‐CBT is feasible to deliver in an outpatient psychiatric setting and may be effective for developing parents' skills and knowledge for coping with PBD, increasing adolescents' psychosocial functioning, and improving family climate. The results are in line with previous findings on CFF‐CBT for children with PBD, suggesting that CFF‐CBT is a valuable adjunctive treatment for adolescents with PBD. Copyright © 2016 John Wiley & Sons, Ltd. Key Practitioner Message Preliminary evidence indicates that CFF‐CBT (RAINBOW) is both acceptable and an important complement to pharmacological treatment for adolescents suffering from paediatric bipolar disorder (PBD). Adolescent PBD populations show a high degree of comorbidity and individual clinical presentations that influence treatment results. Families show a large variation in ability to participate and benefit from RAINBOW treatment. Assessing and addressing pre‐treatment environmental stressors and family climate during treatment is important for optimizing treatment effect. Symptoms of PBD fluctuate and new episodes can occur spontaneously. It is therefore important to follow PBD symptoms over time to draw more precise conclusions on treatment effects. When assessing treatment effects on psychiatric symptoms, social functioning, and family climate, it is important to use multiple rating sources, as ratings can vary considerably between adolescents, parents, and clinicians.