Background: IN our present review, the main goal was to determine the factors that influence the time of CT in diagnosis of SAH in emergency department, since the ED physicians are the first who are approaches to the patients, awareness and attitude of those physicians are very important for the benefit of SAH patients. Methods: We conducted a comprehensive search using following databases; PUBMED, EMBASE, SCOPUS of studies that involving data on the roles and time of CT in diagnosis of subarachnoid hemorrhage (SAH) in ED patients with acute headache, published in English language up to 2017. Conclusion: CT within 6 hours might be considered enough to rule out SAH in the following circumstances: a neurologically regular patient, a thunderclap headache presentation, a clear time of beginning, and a modern-day CT scan carried out within 6 hours of beginning read by a going to radiologist. Time from headache beginning to imaging is reasonably associated with favorable imaging for SAH. Postpone to health center presentation represent the biggest portion of time to imaging, especially those without SAH. These findings recommend restricted opportunity to minimize lumbar puncture rates merely by accelerating in-hospital processes when imaging hold-ups are under 2 hours, as diagnostic yield of imaging decreases beyond the 6-hour imaging window from headache beginning.