A treatment of chronic insomnia is described that is based on the recognition that excessive time spent in bed is one of the important factors that perpetuates insomnia. Thirty-five patients, with a mean age of 46 years and a mean history of insomnia of 15.4 years, were treated initially by marked restriction of time available for sleep, followed by an extension of time in bed contingent upon improved sleep efficiency. At the end of the 8-week treatment program, patients reported an increase in total sleep time (p less than 0.05) as well as improvement in sleep latency, total wake time, sleep efficiency, and subjective assessment of their insomnia (all p less than 0.0001). Improvement remained significant for all sleep parameters at a mean of 36 weeks after treatment in 23 subjects participating in a follow-up assessment. Although compliance with the restricted schedule is difficult for some patients, sleep restriction therapy is an effective treatment for common forms of chronic insomnia.