Patients with suspected fatty liver disease will be screened (and excluded in the presence) of alternative clinical condition associated with NAFLD (see exclusion criteria). Of all patients fulfilling inclusion criteria, relevant baseline characteristics (incl. epidemiological, physiological and biochemical data) will be obtained. In addition, radiological examination will be performed using sonography and fibroscan to assess non-invasively the individual extent of hepatic fat deposition, liver stiffness (fibrosis) and amount of visceral fat mass. In case of high clinical, laboratory and radiological suspicion for NAFLD, a diagnostic liver biopsy will be performed. A part of the liver tissue is used for histological confirmation of NAFLD and subsequent grading and staging according established criteria. Parts of the remaining liver tissue will be stored for later molecular and histological analysis. In addition, several serum samples are collected of patients and stored for future analysis. All patients will be followed up annually (incl. physical examination, metabolic characterisation, clinical chemistry and liver sonography) and additional serum samples will be collected for future analysis. Liver biopsy is not repeated after defined time period, but in case of clinical evidence for disease progression.