In this study, we compared the effect of group and cognitive behavioral treatment (CBT) in clinically referred patients with chronic insomnia. The participants were 32 individually treated primary insomniacs and 74 individuals with either primary or secondary insomnia treated in a group (5-7 patients per group). The primary outcome measures were subjective sleep, quality of life (QOL), and psychological well-being. CBT produced significant changes in sleep onset latency, total sleep time, sleep efficiency, and wake after sleep onset. For total sleep time and sleep efficiency, the improvements were maintained at follow-up as well. In the questionnaires, significant improvements from treatment were seen for the Sickness Impact Profile, Sleep Evaluation Form, and Dysfunctional Beliefs and Attitudes About Sleep. All these improvements remained significant at follow-up. We conclude that CBT for insomnia is effective for both individual and group treatment. Improvements were seen in subjective sleep parameters, QOL, attitudes about sleep, and sleep evaluation in general, both posttreatment and at follow-up.