The aim of this study was to identify the effects of coagulopathy on the outcome of patients with traumatic subdural hematoma (SDH). Based on a retrospective study, the records of all patients admitted between 2001 and 2007 to a large emergency hospital with acute SDH resulting from traumatic brain injury (TBI) were analyzed. An initial Glasgow coma score (GCS), clinical state, and Glasgow outcome score (GOS) were recorded for all patients. All computer assisted tomography and MRI scans obtained from patients were saved on an electronic storage device and were reviewed by a neurosurgeon and a neuroradiologist. The coagulation parameters were analyzed for all patients. Coagulopathy was defined as international normalized ratio more than 1.2 or partial thromboplastin time more than 37 s. One hundred and five women and 214 men aged between 1 and 100 years (mean 59 years) were included in the study. Patients with coagulopathy had a significantly worse outcome. Almost twice as many patients died in the coagulopathy group (mean GOS 3.10 ± 1.46) than in the group without coagulopathy (mean GOS 2.16 ± 1.45), (P < 0.001). In-hospital mortality is twice as frequent in patients with coagulopathy with traumatic SDH compared with noncoagulopathic patients, even if the initial severity of the TBI does not differ.