Researchers have documented widening educational gradients in mortality in the United States since the 1970s. While smoking has been proposed as a key explanation for this trend, no prior study has quantified the contribution of smoking to increasing education gaps in longevity. We estimate the contribution of smoking to educational gradients in life expectancy using data on white men and women ages 50 and older from the National Longitudinal Mortality Study (N = 283,430; 68,644 deaths) and the National Health Interview Survey (N = 584,811; 127,226 deaths) in five periods covering the 1980s to 2006. In each period, smoking makes an important contribution to education gaps in longevity for white men and women. Smoking accounts for half the increase in the gap for white women but does not explain the widening gap for white men in the most recent period. Addressing greater initiation and continued smoking among the less educated may reduce mortality inequalities.