The Japanese Association for Acute Medicine (JAAM) disseminated intravascular coagulation (DIC) study group recently announced new diagnostic criteria for DIC. These criteria have been prospectively validated and demonstrated to progress to overt DIC as defined by the International Society on Thrombosis and Haemostasis (ISTH). Although an underlying condition is essential for the development of DIC, it has never been clarified if patients with different underlying disorders have a similar course. Among 329 patients with DIC diagnosed by the JAAM criteria, those with underlying sepsis (n = 98) or trauma (n = 95) were compared. The 28-day mortality rate was significantly higher in sepsis patients than trauma patients (34.7% vs. 10.5%, p < 0.0001). Within three days of fulfilling the JAAM criteria, sepsis patients had a lower platelet count, higher prothrombin time ratio, higher systemic inflammatory response syndrome score, and higher Sequential Organ Failure Assessment score compared with trauma patients. On day 3, a significantly higher percentage of trauma patients than sepsis patients showed improvement of DIC (64.2% vs. 30.6%, p < 0.001). These differences were mainly due to patients with lower JAAM DIC scores. More than 50% of the JAAM DIC patients with sepsis who died within 28 days could not be detected by ISTH DIC criteria during the initial three days. In contrast, most trauma patients who died within 28 days had DIC simultaneously diagnosed by JAAM and ISTH criteria, except for those with brain death. These findings suggest that coagulation abnormalities, organ dysfunction, and the outcome of JAAM DIC differ between patients with sepsis and trauma.