Rationale: The pathogenetic importance of smoking status in idiopathic pulmonary fibrosis (IPF) is uncertain. In theory, increased oxidative stress in current and former smokers might promote disease progression. However, a better survival has been reported in current smokers in IPF, although this might reflect less severe disease at presentation (a "healthy smoker effect"). Objectives: To determine whether smoking status is associated with survival differences in IPF. Methods: 249 patients with IPF were studied (current smokers, n=20; former smokers, n=166; never-smokers, n=63). Survival was evaluated against smoking status, using proportional hazards analysis, adjusting for gender, age, disease severity [extent of the disease on HRCT, composite physiologic index (CPI), percentage predicted DL_CO in separate models] and the degree of honeycombing. Measurements and Main Results: Current-smokers had milder disease than former smokers, with lower CPI scores (p<0.0001), more extensive disease on HRCT (p<0.005) and a higher unadjusted survival (HR=0.44; 95% CI=0.24, 0.80; p=0.007). However, survival did not differ between current and former smokers (p=0.39) after adjustment for CPI levels. By contrast, the increase in survival is seen in non-smokers than in former smokers (HR=0.51; 95% CI = 0.41, 0.83; p=0.008) was amplified (p<0.0005) by adjustment for CPI levels. Conclusion: In IPF, survival and severity-adjusted survival are higher in non-smokers than in former smokers or the combined group of former and current smokers. By contrast, a better outcome in current smokers, compared to former smokers, reflects less severe disease at presentation and may represent a "healthy smoker effect."