ObjectivesTo evaluate the effectiveness of a short (3 session) programme of group cognitive behavioural therapy (CBT) on insomnia, sleepiness and symptoms of anxiety and depression. MethodsProspective observational study of group CBT with follow-up at 3 months. Participants were self-referred patients with chronic insomnia. Outcome measures were the insomnia severity scale (ISI), the Epworth sleepiness scale (ESS), depression (Pichot scale), and the number of anxiety symptoms. ResultsParticipation in CBT was offered to 489 patients of whom 474 completed the programme and 154 were followed up at 3 months. Significant improvements in insomnia were seen: ISI score (17.74–14.27, P<0.0001) after CBT and at follow-up (13.78, P<0.0001). At the end of CBT, 76% (59/78) with initial severe insomnia and 52% (132/255) with moderate insomnia were improved, maintained at 3 months in 71% (15/21) with severe insomnia and 56% (50/90) with moderate insomnia. Depression and anxiety symptoms were significantly improved: mean depression symptoms (4.15–3.35, P<0.0001) and anxiety symptoms (4.52–3.95, P<0.0001), maintained at 3 months with mean depression symptoms (3.17, P<0.0001) and mean anxiety symptoms (3.62, P<0.0001). Sleepiness increased between baseline and the end of the group (6.67–7.24, P=0.015) followed by a reduction at 3 months (7.19–6.34 at 3 months, P=0.001). Initial ISI score but neither sex nor age were predictive of outcome. ConclusionsA short programme of CBT can improve sleep, depression and anxiety symptoms in self-referred patients suffering from chronic insomnia with good adherence and maximum benefit in patients with severe insomnia.