Nonalcoholic fatty liver disease (NAFLD) is defined as the accumulation of triglycerides (TGs) within hepatocytes exceeding 5 % of liver weight. NAFLD is a spectrum of pathological processes from nonalcoholic fatty liver or simple steatosis to nonalcoholic steatohepatitis (NASH), fibrosis, cirrhosis, and hepatocellular carcinoma. As NAFLD induces metabolic syndrome (MS), then, NAFLD is associated with insulin resistance (IR), type 2 diabetes mellitus (T2DM), hypertension and even Polycystic Ovary Syndrome (PCOS). Because it is well established that patients carrying gene mutations also develop NAFLD in the absence of IR, the genetic predisposition to NAFLD is also discussed. Little is known about the diagnosis and treatment of NAFLD in children and adolescents and the lack of non-invasive diagnostic tools in these populations is a major problem faced by physicians. The present review aims to discuss recent findings of NAFLD in children and adolescents and, considering the features in common with PCOS, we also discuss their relationship.