Background: Severe, abrupt onset headache raises concern for aneurysmal subarachnoid hemorrhage (SAH). The current standard work-up is brain CT scan followed by LP if the CT is non-diagnostic in patients with a normal neurological exam. Some have suggested that angiography is also indicated in this common clinical situation. Is evaluation with brain CT and LP for thunderclap headache to rule out SAH sufficient and is angiography needed? Methods: We systematically searched for studies that followed neurologically-intact patients with thunderclap headache and normal CT and LP for at least 1 year. The primary outcome was SAH. We estimated the proportion of patients who developed SAH and the one-sided upper 95% confidence bound. Results: Seven studies including 813 patients were identified. None of the patients developed SAH during follow-up (pooled proportion = 0, upper 95% confidence bound = 0.004). Conclusion: Although our methods have important limitations, we believe that this analysis will give clinicians better tools to decide whether or not to pursue further work-up with angiography in patients with thunderclap headache and normal neurological exam, CT, and LP. © 2008 Elsevier B.V. All rights reserved.