Non-alcoholic steatohepatitis (NASH) is a part of the spectrum of non-alcoholic fatty liver disease (NAFLD), which can progress to hepatic cirrhosis and end-stage liver disease or hepatocellular carcinoma (HCC). Its pathogenesis is associated with insulin resistance (IR) and the metabolic syndrome. Hepatic steatosis has also been considered an early marker of IR. It is now accepted that NASH is a multistep process with a prominent role for IR, where oxidative stress and cytokines retain a central role. Markers for predicting NAFLD with advanced fibrosis are needed. Once considered irreversible, liver fibrosis is now recognized a dynamic process with significant prospects for remission. The liver biopsy is still a gold standard in assessment of liver fibro-inflammatory activity in the injured liver, but has its own limitations: invasiveness, small tissue sample and inter- and intra-observer error. The lack of non-invasive tests limits the ability of monitoring progression of hepatic fibrosis and response to treatment. Therefore, clinical trials focused on finding of new non-invasive diagnostic tools giving possibilities of frequent, more accurate and reproducible assessment of hepatic fibrosis are constantly conducted.