The term "microvesicular steatosis of the liver" refers to a variant form of hepatic fat accumulation whose histologic features contrast with the much more common macrovesicular steatosis. Microvesicular steatosis of the liver was originally described in association with conditions who share a number of biochemical and a limited number of clinical features: acute fatty liver of pregnancy, Reye's syndrome, Jamaican vomiting sickness, sodium valproate toxicity, high-dose tetracycline toxicity and certain congenital defects of urea cycle enzymes; they were thought to constitute an entity of "microvesicular fat diseases". In recent years the disease has been described in a wide variety of conditions: alcoholism, toxicity of several medications, delta hepatitis in South America and Central Africa, sudden childhood death, congenital defects of fatty acid beta oxidation, cholesterol ester storage disease, Wolman disease and Alpers syndrome. Not much is known regarding the pathogenesis of microvesicular steatosis but in many instances the primary defect could be a mitochondrial lesion, and inhibition of the mitochondrial beta oxidation of fatty acids has been the most frequently implicated defect. The different conditions associated with microvesicular steatosis are heterogenous in many aspects. Maintaining the concept of "microvesicular fat diseases" as a unique entity seems no longer justified.