Background: Insomnia is common in adolescents and often comorbid with psychiatric disorders. This study evaluated changes in insomnia, sleep, and comorbid symptoms following cognitive-behavioral therapy for insomnia (CBT-I) in adolescents with comorbid psychiatric disorders and chronic pain. Methods: In this non-controlled clinical pilot study, participants (n = 23, 78% female) were recruited from adolescent psychiatry and pediatric pain clinics. Assessments of self-reported insomnia, sleep onset latency, wake after sleep onset, total sleep time, sleep efficiency and depression, anxiety, functional disability, and pain intensity were completed at pre- and post-intervention and 3 months follow-up. Results: From pre- to post-intervention, statistically significant improvements were found for insomnia symptoms (p < .001;d = 1.63), sleep onset latency (p < .001;d = 1.04), wake after sleep onset (p < .001;d = 0.38), total sleep time (p = .015;d = 0.22), sleep efficiency (p < .001;d = 1.00), depression (p < .001;d = 0.87), and anxiety (p = .001;d = 0.31). Only eight participants reported data at follow-up with maintained improvements for all measures. Conclusion: This study provides support that insomnia symptoms and sleep can improve following CBT-I delivered in a clinical setting and that co-occurring psychiatric symptoms can be reduced. The results should be interpreted with caution due to the uncontrolled conditions and limited sample size. Well-powered clinical trials are needed to validate the suggested effects.