We studied MR fluid attenuated inversion recovery (FLAIR) pulse sequences in 37 cases with subarachnoid hemorrhage caused by aneurysmal rupture. FLAIR sequence suppressed the CSF signal and produced very heavy T2 weighted images. This has been of particular benefit in identifying lesions at the margins of the brain, around the basal cisterns, in the brain stem and at the gray-white matter junction. Based on these findings, we were able to detect the subarachnoid hemorrhage. Subarachnoid hemorrhage was able to be demonstrated as high signal intensity on FLAIR sequences in all patients. Clear visualization of acute subarachnoid hemorrhage was able to be obtained by MR FLAIR sequences in not only Fisher's group 3 or 4, but also Fisher's group 2. Moreover it was suited for the detection of intraaxial hematoma, Sylvian hematoma, subdural hematoma and subarachnoid hemorrhage in the posterior fossa and interhemispheric fissure. Especially, it was useful for detecting intraventricular hemorrhage. Therefore, if patients suffering from subarachnoid hemorrhage present slight headache or atypical symptoms, sometimes it may be more suitable to perform MRI FLAIR pulse sequences first. Aneurysms were found in 21 cases (56.8%). When the aneurysmal size is more than 7 mm, the rate of detection becomes 100%. Aneurysms present various MR appearances because of flow characteristics. Aneurysms were demonstrated as low signal intensity except in 3 cases. In one out of 3 cases, aneurysms were revealed as high signal intensity and in the other two cases, it was revealed as mixed signal intensity. According to the previous studies, rapid flow was demonstrated as low signal intensity by vascular flow void, and delayed flow was demonstrated as high or mixed signal intensity by flow related enhancement and even echo rephasing. MR clearly delineates the size, the lumen, the flow, and the extraaxial location of aneurysms. In conclusion, MR FLAIR pulse sequences could be reliable and useful for diagnosis of subarachnoid hemorrhage, especially as screening tests for outpatients.