Study Objectives: Insomnia is a prevalent health complaint that often remains untreated. Several interventions are efficacious but they are not widely available. This study evaluated the efficacy of a self-help behavioral intervention for insomnia. Design: The study used a 2 (conditions; self-help treatment, no treatment control) x 3 (assessments; pretreatment, posttreatment, 6-month follow-up) mixed factorial design. Setting: This study was part of a larger epidemiologic study conducted with a randomly selected sample of 2001 adults of the province of Quebec in Canada. Participants: One-hundred ninety-two adults (n = 127 women, 65 men; mean age, 46 years) with insomnia, selected from a larger community-based epidemiologic sample, were randomly assigned to self-help treatment (n = 96) or no-treatment control (n = 96). Interventions: The self-help intervention included 6 educational booklets mailed weekly to participants and providing information about insomnia, healthy sleep practices, and behavioral sleep scheduling and cognitive strategies. Measurements and Results: Participants completed sleep diaries and questionnaires at pretreatment, posttreatment, and 6-month follow-up. Significant but modest improvements were obtained on subjective sleep parameters for treatment but not control participants. Treated participants averaged nightly gains of 21 minutes of sleep and a reduction of 20 minutes of wakefulness, with a corresponding increase of 4% in sleep efficiency. Improvements were also obtained on measures of insomnia severity (Insomnia Severity Index) and of sleep quality (Pittsburgh Sleep Quality Index), and those changes were maintained at follow-up. Conclusions: A self-help behavioral intervention was effective in alleviating a broad range of insomnia symptomatology in a community sample. Self-help may be a promising approach to make effective intervention more widely available.