Insomnia is the most common sleep disorder among the general population. Although cognitive behavioral therapy for insomnia (CBT-I) is the psychological treatment of choice, the availability of individual therapy is often not sufficient to meet the demand for treatment. Group treatment can increase the efficiency of delivery, but its efficacy has not been well-established. Randomized controlled trials (RCTs) comparing group CBT-I to a control group in patients with insomnia were identified. A review of 670 unique citations resulted in eight studies that met criteria for analysis. Outcome variables included both qualitative (e.g., sleep quality) and quantitative (e.g., sleep diary) outcomes, as well as depression and pain severity, at both pre- to post-treatment and follow-up (3-12 mo post-treatment). Overall, we found medium to large effect sizes for sleep onset latency, sleep efficiency, and wake after sleep onset and small effect sizes for pain outcomes. Effect sizes remained significant at follow-up, suggesting that treatment gains persist over time. Other variables, including total sleep time, sleep quality, and depression, showed significant improvements, but these findings were limited to the within treatment group analyses. It is clear that group CBT-I is an efficacious treatment. Implications for stepped care models for insomnia are discussed