A new case of congenital dysfibrinogenemia has been discovered in a 20 year old woman, who suffered from a severe postpartal hemorrhage after the delivery of her first child, followed by episodes of thrombosis. Coagulation studies reveal a prolongation of thrombin time, reptilase time was immeasurable. Thromboplastin time and partial thromboplastin time were slightly prolonged. Low fibrinogen levels were obtained by techniques, which depend on the coagulation velocity following addition of thrombin, while immunological procedures gave slightly diminished values of fibrinogen. Patients's fibrinogen had a moderate inhibitory effect on the fibrin formation in normal plasma. However, inhibitors of the fibrinogen-fibrin conversion could not be detected. Coagulation factors were normal, fibriolysis as well. The cause of the coagulation disorder was found to be a defect of the fibrinogen molecule, leading to an abnormal fibrin polmerization of patient's fibrin monomers. The release of the fibrinopeptides in the paperelectrophoresis was normal. The defect of the fibrinogen molecule did not protect from thrombotic complications. The same defect could be found in the lower scale in patient's father, 4 of her 7 brothers and sisters, and her son.