OBJECTIVE: Cognitive-behavioral therapy for insomnia (CBT-I) is recognized as the first-choice intervention for insomnia. One of the best-known advantages of CBT-I in comparison with pharmacotherapy is its long-term effect. However, only few studies have assessed its benefits with follow-up periods of longer than three years. In this clinical case series study we aimed to describe the long-term effects of group CBT-I after a mean 7.8 ± 1.6 years of follow-up (range 4-10 years). METHODS: A total of 292 insomnia disorder (ID) patients were consecutively enrolled at the Sleep Disorders Center of San Raffaele Hospital, Milan; 123 patients (82 (66.7%) females and 41 (33.3%) males, mean age 40.59 ± 11.89 years) completed the follow-up evaluation within a range of 4-10 years. RESULTS: In the 258 patients who completed the treatment, insomnia severity index (ISI) total score improved significantly as well as all variables of the sleep diaries. Using ISI as the primary outcome, we demonstrated that the effect of CBT-I is maintained up to 10 years after the end of treatment. Furthermore, we found that patients that used only CBT-I techniques to deal with relapses were the ones with better outcomes, in particular compared to the patients that re-used medications. CONCLUSION: To the best of our knowledge this is the longest follow-up evaluation in the literature, both for group and individual CBT-I. These findings have an important clinical implication both suggesting and confirming that CBT-I can be considered the treatment of choice for insomnia. Copyright © 2018 Elsevier B.V. All rights reserved.