['A high prevalence of obstructive sleep apnea syndrome (OSAS) has been reported in severely obese patients with nonalcoholic fatty liver disease (NAFLD), but few studies have evaluated OSAS in non-morbidly obese NAFLD patients.', 'To determine the prevalence of risk for OSAS with or without daytime sleepiness in non-morbidly obese patients with NAFLD and evaluate the association with the severity of liver damage.', 'We considered 159 consecutive patients with histological NAFLD and body mass index (BMI) <35 Kg/m2, and 80 controls without ultrasonographic steatosis matched for age, sex, and BMI. OSAS risk was determined by positivity for Berlin questionnaire (BQ), and daytime sleepiness by the Sleepness Epworth Scale (ESS). Liver damage was evaluated according to the NAFLD activity score.', 'In NAFLD patients, BQ alone was positive in 39 (25%), ESS in 8 (5%), and both in 13 (8%, OSAS with sleepines); p\u200a=\u200ans vs. controls without steatosis. In NAFLD patients at risk for OSAS with (but not in those without) sleepiness, we observed a higher prevalence of nonalcoholic steatohepatitis (NASH; 11/13, 85% vs. 72/146, 49%; p\u200a=\u200a0.018), and of clinically significant fibrosis (stage>1; 9/13, 69% vs. 39/146, 27%; p\u200a=\u200a0.003). At multivariate logistic regression analysis, OSAS with sleepiness was strongly associated with NASH and fibrosis>1 independently of known clinical risk factors such as age, gender, BMI, diabetes, and ALT levels (OR 7.1, 95% c.i. 1.7-51, p\u200a=\u200a0.005 and OR 14.0, 95% c.i. 3.5-70, p\u200a=\u200a0.0002, respectively).'] Is risk of obstructive sleep apnea with daytime sleepiness associated with liver damage in non-morbidly obese patients with nonalcoholic fatty liver disease?