OBJECTIVE: Insomnia affects patients' quality of life and workplace productivity, and is a risk factor for costly acute events and chronic diseases. Existing data on the costs of insomnia are sparse and outdated. Accordingly, in this study we estimated current societal and employer costs of chronic primary insomnia in the U.S. METHODS: Prevalence-based cost-of-illness estimation techniques and data from secondary sources were used to assess the economic burden of chronic primary insomnia (i.e., insomnia that is not due to a medical, psychiatric, or environmental cause) in the U.S. population. Costs included insomnia medications, insomnia-attributable health events and chronic conditions (i.e., depression, alcohol abuse, nicotine dependency, drug abuse, accidental injuries), and lost productivity. The cost of each insomnia-attributable health consequence was estimated by multiplying its total cost by its population attributable risk, which is a function of the prevalence of chronic primary insomnia and the relative risk of the health consequence in persons with versus without insomnia. Based on published sources, we estimated the prevalence of chronic primary insomnia to be 2.3% and relative risks to be as follows: car crashes, 2.5; work accidents, 1.5; home/public accidents, 2.5; alcohol abuse, 2.3; illicit drug abuse, 1.9; nicotine dependency, 2.4; and depression, 5.4. RESULTS: Total annual societal cost of chronic primary insomnia in the U.S. was estimated to be US$24.6 billion in 2003. Depression accounted for the largest share of the cost burden (34%), followed by alcohol abuse (25%), nicotine dependency (20%), drug abuse (14%), work loss (6%), accidental injuries (2%), and prescription insomnia medications (1%). Sensitivity analysis indicated the findings were most sensitive to the prevalence of chronic primary insomnia and the relative risk of illicit drug abuse. CONCLUSIONS: The economic burden of chronic primary insomnia is substantial. Reducing the severity and prevalence of chronic primary insomnia may yield considerable economic benefits.