Although spontaneous subarachnoid hemorrhage has been extensively studied from various standpoints, few reports have assessed changes in the hemostatic system occurring in association with SAH. Patients with aneurysm bleeding usually do not have deficient coagulation system; instead sudden local bleeding occurs at site where the vascular wall has ruptured because of structural and proteolytic disturbances. In patients with aneurysm bleeding, in which various amounts of blood are in contact with extravascular matrix, changes m the hemostatic system are poorly understood. · The author examinated serial markers of thrombin generation (thrombin-antithrombin complex) and subsequent fibrinolysis (D-dimer) and studied their associations with the severity of the disease during the acute phase after SAH, computed tomographic findings, the incidence of delayed ischemie deficit and with outcome. The data suggest that the activation of the blood coagulation system as well as of the fibrinolytic system occurred early in the course of SAH. These systems were activated to a greater extent m patients m poorer clinical stage on admission, greater amount of subarachnoid blood seen on CT and poorer clinical outcome. Levels of TA T and fibrinogen are independent factors associated with death and poor outcome. Hemostatic measurements <lid not predict delayed ischemie deficit in this population.