Two young siblings (a male of 21 and his sister of 26 years) suffered from arterial thrombosis episodes of the carotid and abdominal aorta documented by angiographic studies. In the absence of any known predisposing factor in the family and personal history, the laboratory investigation of both patients revealed coagulation abnormalities compatible with a dysfibrinogenemia. The occurrence of a similar defect also in plasma of one of the propositi's asymptomatic relatives is suggestive of an inherited fibrinogen disorder.