Both cryptogenic liver cirrhosis and idiopathic portal hypertension without pathological findings of liver cirrhosis (IPH) are relatively common in Japan. To find differrence between IPH and cryptogenic liver cirrhosis of Japanese, we investigated human leukocyte antigen (HLA), familial clustering of liver diseases as well as prevalence of HBs antigen in 31 patients with IPH. The age of patients with IPH ranged between 6 and 67 years old (mean, 40 years). The ratio of female to male in patients with IPH was 3.1. The incidence of chronic liver diseases in the relatives of patients with cryptogenic liver cirrhosis was significantly high (29.1%), whereas that in the relatives of patients with IPH was not high (12.9%) as compared with hospitalized controls (8.9%). The phenotype frequencies of the specificities of HLA A and B loci in patients with IPH did not differ from those in healthy controls. And the incidence of HBs antigen and antibody in patient with IPH (3.2% and 20.7%, respectively) was similar to those in normal subjects in Japan. These findings suggest that IPH in Japan is a different clinical entity from cryptogenic liver cirrhosis and that HB virus may not be one of the main causes of IPH.