OBJECTIVE The authors investigated whether self-reported life satisfaction predicted suicide over a period of 20 years (1976-1995) in adults unselected for mental health status. METHODS A nationwide sample of adults aged 18-64 years (N=29,173) from the Finnish Twin Cohort responded to a health questionnaire that included a life satisfaction scale (score range=4-20, with higher scores indicating greater dissatisfaction) that covered four items: interest in life, happiness, general ease of living, and feeling of loneliness. "Dissatisfied" subjects (life satisfaction score=12-20) were compared to "satisfied" subjects (score=4-6). Mortality data were derived from the national registry and analyzed with Cox regression. RESULTS Dissatisfaction at baseline (life satisfaction score=12-20) was associated with a higher risk of suicide throughout the 20-year follow-up period (age-adjusted hazard ratio=3.02, 95% confidence interval [CI]=1.83-4.98). The association was somewhat stronger in the first decade (hazard ratio=4.46, 95% CI=1.95-10.20) than in the second (hazard ratio=2.34, 95% CI=1.24-4.45). A dose-response relationship was also found. Men with the highest degrees of dissatisfaction (life satisfaction score=19-20) were 24.85 times as prone to commit suicide as satisfied men during the first 10 years of the follow-up period. Throughout the entire follow-up, life dissatisfaction still predicted suicide after adjusting for age, sex, baseline health status, alcohol consumption, smoking status, and physical activity (hazard ratio=1.74, 95% CI=1.02-2.97). Subjects who reported dissatisfaction at baseline and again 6 years later showed a high suicide risk (hazard ratio=6.84, 95% CI=1.99-23.50) compared to those who repeatedly reported satisfaction. CONCLUSIONS Life dissatisfaction has a long-term effect on the risk of suicide, and this seems to be partly mediated through poor health behavior. Life satisfaction seems to be a composite health indicator.