The aim was to study whether occasional smoking increases mortality risk. The mortality of random samples of the Finnish Adult Health Behavior surveys from 1978 to 1991 were followed for 18 years from 1978 to 1995. Poisson models were used to determine the risk of total and cardiovascular mortality. It was found that occasional smokers were less often sedentary and had less often unhealthy diet than other smoking status groups. Occasional smoking among men was significantly related to the risk of both total (age-adjusted relative risk, RR, 1.6, 95% confidence interval, CI, 1.3-2.1) and cardiovascular mortality (age-adjusted RR 1.5, 95% CI 1.0-2.3). Controlling for education, period and chronic morbidity did not change results. Among women no significant associations could be established; when adjusted for age, period, education and morbidity the RR for cardiovascular mortality was 1.4 (95% CI 0.6-3.4) and total mortality 1.0 (95% CI 0.6-1.6). Occasional smoking is associated with increased risk of premature death, at least among men. Although occasional smoking is a less dangerous practice than regular smoking, it is not a safe alternative for daily smoking.