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Objective:The aim of this retrospective clinical study is to provide a proper management strategy for patients who present spontaneous subarachnoid emorrhage(SAH) with negative initial angiogram by investigating the clinical features, long-term outcomes and radiologic characteristics. Methods : One hundred and twenty-eight out of 2887 SAH patients who were admitted to neurosurgery department from 1986 to 2002 had negative initial angiogram. We classified the 128 patients into 3 groups(Group I : no evidence of SAH on CT but confirmed by lumbar puncture, Group II: perimesencephalic(PM) SAH pattern, Group III: non-perimesencephalic(NPM) SAH pattern), and reviewed the radiologic findings, the clinical features, the rebleeding rate, the long-term outcome, and the results of repeated angiogram. Factors related to the false negative initial angiogram were also reviewed. Results : The patients were 9(7.0%) in Group I, 85(66.4%) in Group II, and 34(26.6%) in Group III. There was no difference in long-term clinical outcome. Ninety-two out of 128 patients underwent a repeated angiogram in which 18 patients were found to have ruptured aneurysms that were not detected on the initial angiogram(false negative rate: overall 19.6%, 1.8% in Group II, 50.0% in Group III). Small size(<6mm) aneurysms, spasms, hematomas, and anterior communicating aneurysms were the factors affecting false negative initial angiogram. Conclusion : In SAH patients with negative initial angiogram, espeacially those who had a non-perimesencephalic SAH pattern on initial CT findings, a repeated angiogram should be considered for identifying the hidden ruptured aneurysm. Key words:Subarachnoid hemorrhage;CT findings;Cerebral angiogram;False negative.