The diagnosis of subarachnoid hemorrhage remains difficult to establish, yet the sensitivity of increasingly available 16-detector computed tomography (CT) has not been evaluated. The objective of this study was to estimate the sensitivity of 16-detector CT for the diagnosis of non-traumatic subarachnoid hemorrhage in the Emergency Department (ED). A retrospective review was performed in an academic tertiary care hospital. Patients presenting to the ED from September 2003 through December 2004 with symptoms suggestive of subarachnoid hemorrhage and having a final diagnosis of non-traumatic subarachnoid hemorrhage were eligible for study. Diagnosis was established by positive 16-detector CT examination of the brain, or spinal fluid analysis. Patient demographics and results of CT, angiogram, and spinal fluid analysis were reviewed. Sensitivity of 16-detector CT was calculated by comparing CT results and cerebral angiogram results. Refined Wilson Simple Asymptotic 95% confidence intervals were calculated. Sixty-one consecutive patients met the study criteria and had a final diagnosis of non-traumatic subarachnoid hemorrhage. One of these patients did not have subarachnoid hemorrhage identified by 16-detector CT, but had a positive lumbar puncture and an aneurysm confirmed on cerebral angiography. Sensitivity of 16-detector CT for subarachnoid hemorrhage was 97% (95% confidence interval 84-100%). Sixteen-detector CT did not improve detection of non-traumatic subarachnoid hemorrhage when compared with studies using single-detector CT. If there is high clinical suspicion for non-traumatic subarachnoid hemorrhage and non-contrast 16-detector CT scan is negative, further evaluation is suggested.