A sign of descending tentorial herniation (DTH) on computed tomography (CT) in 48 patients with putamenal hemorrhage was examined in the acute stage. Correlation between the DTH sign and prognosis for survival was studied in two groups; a conservative group and an operative group. Patients were grouped according to the presence or absence of DTH sign on CT. Grade 0: no herniation sign; Grade I: an encroachment upon the lateral aspect of the suprasellar cistern (impending herniation); Grade II: widening of the crural and ambient cistern on the same side as hematoma (actual herniation); Grade III: effacement of the cisternal space at the tentorial level (advanced stage of herniation). Twenty-one patients (44%) with Grade 0 DTH sign showed a good prognosis in both conservative and operative groups. Six patients (13%) with Grade I DTH sign also showed a good prognosis in both the conservative and the operative groups except one patient with anisocoria. There were 14 patients (29%) with Grade II DTH sign. Three of them who were treated conservatively showed only mild impairment of consciousness at the initial phase, but became worse 3-4 hours later. In the remaining patients who showed severe impairment of consciousness from the beginning of the illness, prognosis was poor except for patients with hematoma evacuation. Seven patients (15%) with Grade III DTH sign had poor prognosis both in the conservative and the operative groups. It is suggested that, in the acute stage of patients with putamenal hemorrhage, operative procedure should rapidly be performed not only for the clinical herniation sign but also for the DTH sign on CT even if the patients showed no clinical sign and only impairment of consciousness.