Non-alcoholic liver disease is associated with the metabolic syndrome especially obesity and diabetes mellitus. It has been noted that a fraction of NAFLD patients are not obese and in fact may even have a BMI that is within the "lean" criteria. Rather than a separate disease with different pathogenesis, most studies have supported that "lean" or "non-obese" NAFLD represent a spectrum of NAFLD where there are similar metabolic drivers even though the BMI may not be increased. Despite the assumption that the NAFLD is milder, these patients may go on to develop advanced liver fibrosis and even HCC. Non-invasive markers of liver fibrosis are being validated in this population. Management principles of of NAFLD remain the same. Although no weight loss may be needed, exercise does improve the liver condition. Understanding the drivers in this group of patients will provide deeper understanding of the pathogenesis of NALFD.