A comparison was made between factors influencing survival in patients operated on for acute spontaneous subdural hematomas (ASSH) and other groups of patients operated for acute, post-traumatic, subdural hematoma reported in the literature. The data of 17 patients operated on for ASSH were collected. Four variables: early surgical treatment, high Glasgow Coma Scale score on admission, pupillary reactivity and age were statistically analyzed. The most significant factors for good outcome, in order of importance, were early surgical treatment, a high Glasgow Come Scale score on admission, good pupillary reactivity and younger age. The prognostic factors in non-traumatic and traumatic acute subdural hematomas were found to be identical.