The authors presented a case of a subacute epidural hematoma of the posterior fossa, for which we never thought of a head injury at the admission. We discussed the diagnosis (the clinical pictures and X-ray findings), stressing that CT plays an important role especially in diagnosing posterior fossa diseases. Our case could probably not be diagnosed correctly without CT, because the conventional X-ray examinations did not reveal clearly the space--occupying lesion in the posterior fossa, before CT was done. The following findings can be a clue to diagnose a posterior fossa hematoma: 1. occipital fracture (which was not found in our case) or suture diastasis, occipital scalp contusion, 2. progessive conscious disturbance, cerebellar and brain stem signs, pyramidal sigs and neck stiffness, 3. a patient has a tendency to lie on the side, especially on the lesion side. On angiography, substraction films must be obtained especially for the posterior fossa diseases. The posterior fossa veins of our case were opacified less on the left than on the right, and the left transverse sinus was apparently amputated in its opacification. These findings were due directly to the compression of the epidural hematoma. CT can promptly not only a posterior fossa hematoma, but also accompanied supratentorial lesions (concrecoup injury etc) simultaneously, therefore one can expect that there are not errors any more with CT to overlook the supratentorial contrecoup injury. Posterior fossa hematomas have usually a venous bleeding origin, from the transverse sinus, torcular Herophilli, emissary veins, bridging vein etc. therefore, present a slowly progressive and intermittent neurological signs, as the hematomas grow slowly.