Nonalcoholic fatty liver disease (NAFLD) is an increasing public health threat with significant related morbidity and mortality. NAFLD is currently separated into two clinical entities, benign simple steatosis, and NASH, the more progressive form. Instead, NAFLD is likely a spectrum of disease that can progress regardless of the initial histologic findings. Risk factors associated with disease progression of NASH include the histologic findings of lobular inflammation, presence of NASH rather than simple steatosis, and most significant, the presence of fibrosis. In addition, comorbid metabolic conditions such as type 2 diabetes mellitus, obesity, and metabolic syndrome play a significant role in progression, and sometimes regression, of NAFLD. Currently liver biopsy remains the gold standard for diagnosis and staging of NAFLD, however noninvasive testing is garnering more interest in ongoing research trials and will hopefully prove to be a reliable means of evaluating patients with NAFLD in the future.