Aim:The aim of this study is to report our experience with a relatively large series of patients with NNSAH to identify the prognosis associated with different bleeding patterns as well as a further diagnostic work-up to determine the underlying cause. Material and Methods:Between January 2004 and December 2014, 81 patients with angiography-negative nontraumatic subarachnoid hemorrhage (SAH) were treated at our institution. Diagnosis was confirmed with a typical history of spontaneous SAH and cranial computed tomography (CT) scan or lumbar puncture (LP). The patients were grouped according to the bleeding pattern on the CT scan: Group 1) Perimesencephalic (PM) SAH (n:33, 40.7%), Group 2)Non-perimesencephalic (nPM) SAH (n:41, 50.6%), and Group 3) CT- negative NNSAH (n:7, 8.6%). The clinical course, hospitalization period, and complications were noted. All patients underwent an initial four-vessel digital subtraction angiography (DSA). Cranial magnetic resonance imaging (MRI), repeat DSA investigations and spinal MRI were performed in all patients.Results:The mean hospital stays were 6.3, 14.7 and 10.1 days for patient groups 1, 2, and 3, respectively. The mortality rate was 1.2% (1 patient) in our series. Repeat DSA investigations were positive in two patients (2.5%), both from Group 2 (4.9%). Cranial MRI revealed 100% negative results. Spinal MRI revealed positive results in three patients from Group 2 (7.3%).Conclusion:We suggest our diagnostic work-up for patients with nPM-SAH, namely repeat DSA and spinal MRI, until an evidence-based guideline is established for the patient management.