Background: The severity of liver injury and clinical outcomes in lean NAFLD subjects is a subject of debate and very few studies have been performed in the general population. The aim of this study was to compare subject characteristics and mortality between lean and non-lean NAFLD in a community setting. Method: The study population included 169,303 participants from the nationwide Constances cohort. Subjects with excessive alcohol consumption, viral hepatitis or other liver diseases were excluded and 137,206 subjects were analyzed. The diagnosis of NAFLD and fibrosis was performed using the Fatty Liver Index and the Forns Index. The median follow-up was 3.58 years. Results: The prevalence of NAFLD was 5.3% (95%CI 5.2-5.4) in lean subjects, while 16.3% (95%CI 15.7-16.8) of NAFLD subjects were lean. Despite their better metabolic profile, the prevalence of advanced fibrosis was significantly higher in lean than in non-lean NAFLD (3.7% vs. 1.7%, respectively P<0.01). Among NAFLD subjects and after adjustment for demographics, metabolic risk factors and lifestyle, lean status was associated with advanced fibrosis (0R=1.26, 95%CI 1.20-1.65, P=0.005), an increased risk of liver-related events (aHR=5.84, 95%CI 4.03-8.46), chronic kidney disease (aHR=2.49, 95%CI 1.49-4.16), and overall mortality (aHR=3.01, 95%CI 2.21-4.11). Liver-related events and overall mortality were related to the severity of fibrosis, both in lean and non-lean NAFLD subjects, whatever the usual risk factors. Conclusion: This study in a large community-based cohort confirms that NAFLD in lean subjects is more severe for fibrosis, the progression of liver disease, chronic kidney disease and overall mortality.