SummaryThree patients in the same family with low fibrinogen levels have been studied. The abnormality was clinically silent. The fibrinogen level varied from 50 to 145 mg/dl. Good agreement between the various methods of fibrinogen assay was observed. Since no afibrinogenemic patient was observed in this family, the abnormality presented by these patients was classified as congenital hypofibrinogenemia. Our observation also suggests that there is an increase in fibrinogen level with age in hypofibrinogcnemic patients, as occurs in normal subjects.