Widespread unhealthy dietary habits associated with a sedentary lifestyle have made NAFLD the most frequent chronic liver disease worldwide, with a global prevalence of ~25%. Although NAFLD is mainly considered to be a benign disease, it can progress to severe liver fibrosis and hepatocellular carcinoma (HCC), with the latter found in non-cirrhotic livers in about 40% of cases. Factors favouring the progression of liver disease in NAFLD are only partially understood. Male sex, older age and Caucasian ethnicity have frequently been identified as factors accelerating the progression of fibrosis in NAFLD, although data are not consistent. Host genetic variants appear to be very important, especially in the gene coding for the patatin-like phospholipase domain-containing 3 (PNPLA3), and they may also play a role in the development of HCC, independent of activity and the extent of liver damage. However, the most important factors affecting disease progression are found in the metabolic syndrome, that is, obesity, type 2 diabetes and arterial hypertension. This mini-review will discuss the contribution of these factors to NAFLD-associated morbidity, emphasizing the importance of preventive measures such as physical activity and weight control in view of the current pandemic of the metabolic syndrome.