Forty‐two Japanese families, including 80 individuals with Werner's syndrome were studied, confirming that this syndrome is inherited as an autosomal recessive trait. The incidence of malignancy was relatively high in these families and individuals with Werner's syndrome, although the incidence was not so high as was reported previously. HLA typing revealed no significant linkage with Werner's syndrome. The frequency of Werner's syndrome in Japan was estimated using two methods which indicated approximately 300 cases among 100 million peopl