Worldwide, an estimated 189 million adults smoke tobacco "occasionally" but not every day. Yet few studies have examined the health risks of non-daily smoking. Data from the 1991, 1992, and 1995 U.S. National Health Interview Surveys, a nationally representative sample of 70,913 U.S. adults (aged 18-95 years) were pooled. Hazard ratios and 95% CIs for death through 2011 were estimated from Cox proportional hazards regression using age as the underlying time metric and stratified by 5-year birth cohorts in 2017. Non-daily smokers reported smoking a median of 15 days and 50 cigarettes per month in contrast to daily smokers who smoked a median of 600 cigarettes per month. Compared with never smokers, lifelong nondaily smokers who had never smoked daily had a 72% higher mortality risk (95% CI=1.36, 2.18): higher risks were observed for cancer, heart disease, and respiratory disease mortalities. Higher mortality risks were observed among lifelong non-daily smokers who reported 11-30 (hazard ratio=1.34, 95% CI=0.81, 2.20); 31-60 (hazard ratio=2.02, 95% CI=1.17, 3.29); and >60 cigarettes per month (hazard ratio=1.74, 95% CI=1.12, 2.72) than never smokers. Median life-expectancy was about 5 years shorter for lifelong non-daily smokers than never smokers. As expected, daily smokers had even higher mortality risks (hazard ratio=2.50, 95% CI=2.35, 2.66) and shorter survival (10 years less). Although the mortality risks of non-daily smokers are lower than daily smokers, they are still substantial. Policies should be specifically directed at this growing group of smokers.