Nodular regenerative hyperplasia (NRH), a rare hyperplastic condition of the liver, is reported in two patients with primary pulmonary hypertension (PPH). The first patient was a 26-year-old man who died of PPH and showed multiple NRH without cirrhosis of the liver. The second patient was a 25-year-old man who had a PPH with pulmonary arterial thrombi and NRH of the liver. NRH has been described in association with immune disease, hematopoietic disorder, and diabetes mellitus, so that NRH with PPH is considered to be very rare. Histologic findings of the lungs show typically plexogenic pulmonary arteriopathy in both cases, and the livers of these patients are composed of multiple nodules that are histologically represented by slightly larger hepatocytes arranged in a cobblestone-like fashion, and are ultramicroscopically characterized by massive proliferation of mitochondria. The pathogenetic association of nodular regenerative hyperplasia with primary pulmonary hypertension will be discussed.