Objective: To evaluate a protocol for acceptance and commitment therapy-based behavioral intervention for insomnia (ACT-BBI-I) in adults compared to cognitive behavioral therapy for insomnia (CBT-I). Methods: Forty-five adults with chronic insomnia were randomized to ACT-BBI-I or CBT-I. Both interventions were performed in six weekly group sessions. The common treatment elements in both protocols included stimulus control and sleep restriction. CBT-I is focused on the cognitive restructuring of maladaptive beliefs about sleep and the daytime effects of insomnia. ACT-BBI-I focuses on therapeutic processes of acceptance, availability, values, defusion, and commitment. The results were evaluated through the following instruments: a sleep diary, the Insomnia Severity Index, the Epworth Sleepiness Scale, the Hospital Anxiety and Depression Scale, the Acceptance and Action Questionnaire-II, and the Dysfunctional Beliefs and Attitudes about Sleep scale. Results: Both interventions had a significant positive impact on sleep patterns, insomnia, anxiety, beliefs about sleep, and psychological flexibility. All improvement was maintained at the 6-month follow-up. Conclusion: The results suggest that integrating principles of ACT with behavioral techniques may be useful for treating insomnia. Further research should identify whether the principles of ACT result in added effectiveness compared to behavioral components alone. Clinical trial registration: RBR-7nc5wq