Early diagnosis is necessary for the treatment of disseminated intravascular coagulation (DIC), but criteria for the stage preceding the diagnosis of DIC (pre-DIC) have not yet been established. To clarify hemostatic abnormalities that occur before the onset of DIC, we performed hemostatic studies in 117 patients within at least a week before the onset of DIC (pre-DIC), in 237 patients with DIC, and in 50 patients without DIC or pre-DIC (non-DIC). Levels of FDP, PT, and fibrinogen, and platelet counts were significantly abnormal after the onset of DIC, but not before. Thrombin-antithrombin III complex (TAT), plasmin-alpha 2 plasmin inhibitor complex (PIC), and FDP-D-dimer levels were significantly higher before the onset of DIC compared to the non-DIC patients. Hemostatic abnormalities were observed within a week before the onset of DIC. Monitoring the plasma levels of TAT, PIC, and FDP-D-dimer might be useful for the diagnosis of a pre-DIC condition.