Objective Little is known about how participation in internet-based behavioral interventions influences outcomes in youth with health conditions. This study describes participation in an online behavioral pain management intervention for families of adolescents with chronic pain. Methods 26 adolescent–parent dyads were randomized to the intervention arm of a controlled trial evaluating a cognitive–behavioral pain intervention. Participation was measured by the number of logins, messages, completion of interactive fields, and behavioral assignments. Associations between content of messages from participants and treatment outcomes were evaluated. Results Most participants (92.3%) logged in and completed assignments. Over half of participants initiated messages to the online coach. A greater number of messages sent by adolescents containing rapport or treatment content predicted positive treatment outcomes. Conclusions Most families actively participated in the intervention. Interaction with an online coach may increase the benefit of this Internet behavioral pain management treatment program for adolescents.