The objective was to study physical therapists' (PTs') experiences of learning and delivering a complex intervention, a tailored behavioral medicine treatment (BMT) targeting adolescents with pain in primary care. Method: An explorative study with qualitative approach, using content analysis. Three primary care PTs delivering the treatments in a randomized controlled study were interviewed regarding their views on the BMT. Results: The participating PTs considered learning about and delivering the BMT as challenging but rewarding. The biopsychosocial approach, tailoring of the treatment and dialogues with parents were identified as key aspects of the BMT program. The process of formulating a functional behavioral analysis was perceived as strenuous. The supervision of the PTs throughout the study was regarded as crucial and necessary for learning about and providing tailored BMT. Conclusion: Learning about and delivering BMT targeting adolescents with persistent pain is fruitful but laborious and demanding according to three PTs experienced with treatment of pediatric pain in primary care. Extensive education and long periods of supervision seem to be crucial for success and safe delivery according to protocol.