The purpose of the study was to investigate the natural history of insomnia and its association with depression and mortality. In 1983, 1,870 randomly selected subjects aged 45-65 years answered a questionnaire on sleep and health. Of the 1,604 survivors in 1995, 1,244 (77.6%) answered a new questionnaire with almost identical questions. Mortality data were collected for the 266 subjects that had died during the follow-up period. Chronic insomnia was reported by 36.0% of women and 25.4% of men (chi2 = 9.7; p < .01). About 75% of subjects with insomnia at baseline continued to have insomnia at follow-up. Insomnia in women predicted subsequent depression (odds ratio [OR] = 4.1; 95% confidence interval [CI] 2.1-7.2) but was not related to mortality. In men, insomnia predicted mortality (OR = 1.7; 95% CI 1.2-2.3), but after adjustment for an array of possible risk factors, this association was no longer significant. Men with depression at baseline had an adjusted total death rate that was 1.9 times higher than in the nondepressed men (95% CI: 1.2-3.0).