Objectives. To evaluate the efficacy of cognitive behavioral therapy (CBT-I) for chronic insomnia treatment. Method. The 236 patients with ICD-10 nonorganic insomnia were assigned to group CBT-I (6 sessions, 6-10 patients). From this pool, 72 participants with no history of other psychiatric or sleep disorders conditions were selected. Eventually, 51 patients (40f, mean age: 54.6 +/- 13.9y, mean insomnia duration: 7 +/- 6.3y) and 51 matched healthy controls (mean age: 55.4 +/- 14.3y) completed the study. Outcomes in the insomnia group at baseline and post-treatment were compared to control group. Subjects underwent sleep diary, the Athens Insomnia Scale (AIS), the Beck Depression Inventory (BDI), the Ford Insomnia Response to Stress Test (FIRST), the SF-36 questionnaire and the State-Trait Anxiety Inventory (STAI). Results. At baseline, groups differed significantly in most dependent variables. At post-treatment, a substantial improvement in all sleep parameters was observed in insomnia group: sleep latency, number of awakenings, wake time after sleep onset, sleep time, sleep efficiency, sleep quality and frequency of hypnotic use. These outcomes were accompanied by lower AIS and FIRST scores, reductions of depression and anxiety symptoms, and improved energy and social functioning ratings. All changes were maintained during the 3-month follow-up. Only 10/51 patients had no clinically meaningful improvement at any post-treatment time points. After the therapy, patients did not differ significantly from good sleepers in number of awakenings, sleep quality, feeling in the morning, depression and anxiety symptoms, and quality of life related to mental health. Conclusions. The CBT-I produced a sustained, clinically meaningful improvement in nocturnal sleep and daytime functioning.