DefinitionNodular regenerative hyperplasia (NRH) of the liver is an uncommon condition characterized by the diffuse transformation of normal hepatic parenchyma into small, regenerative nodules with little to no fibrosis. A classification system proposed by Wanless in 1990 1 provided histological criteria for the diagnosis of NRH. These included the presence of hepatocellular nodules less than 3 mm in diameter that were not surrounded by fibrosis (nodules graded 0-3ϩ based on the extent of nodularity noted through all fields of the biopsy), and the presence of fibrous septa (graded 0-3). Biopsy specimens that met the criteria of 3ϩ nodularity and 0-1 fibrous septa were classified as nodular regenerative hyperplasia. NRH has been reported to occur in association with other systemic diseases, including rheumatologic disorders, vascular disorders, and myeloproliferative disorders, as well as certain drugs. 1-10 Nodular regenerative hyperplasia may have a prolonged asymptomatic course unless it is complicated by portal hypertension and its sequelae, including variceal bleeding, ascites, and splenomegaly. In this article, the epidemiology, histology, differential diagnosis, and theories of etiology of NRH are reviewed. The diagnosis and treatment of nodular regenerative hyperplasia are also presented.