PURPOSE: To evaluate the clinical usefulness and limitation of FLAIR (fluid attenuated inversion recovery) MR sequence in various intracranial pathologic conditions. MATERIALS AND METHODS: In prospective fashion, we used a 1.0T MR unit to obtain FLAIR sequence MR images, together with T1-weighted (TIWI), proton-density weighted (PDWI), and T2-weighted spin echo images (T2WI) in 24 patients with various intracranial diseases. Forty-two lesions in 24 patients were classified into three categories: nonhemorrhagic noncavitary lesions (n=20), hemorrhagic lesions (n=10), and cavitary lesions (n=12). Hemorrhagic lesion was divided into two types; type 1 showed high signal intensity on both T1WI and T2WI and type 2 showed marked low signal intensity on T2WI such as hemosiderin. Cavitary lesion was defined as one with signal intensity which paralleled CSF on all pulse sequences. Visually, we compared the lesion conspicuity on FLAIR with that on T2WI. Quantitatively, we also compared lesion/white matter (WM) contrast, lesion/WM contrast to noise ratio (CNR), lesion/CSF contrast, and lesion/CSF CNR on FLAIR with those on T2WI. RESULTS: For visual conspicuity of nonhemorrhagic noncavitary lesions and type 1 hemorrhagic lesions, FLAIR was superior to PDWI and T2WI, but for type 2 hemorrhangic lesions, PDWI and T2WI were superior to FLAIR. For cavitary lesions, there was no significant difference between T2WI and FLAIR. In the quantitative assessment of nonhemorrhagic noncavitary lesions, FLAIR was superior to PDWI for lesion/CSF contrast, and CNR, and lesion/WM contrast, but for lesion/WM CNR FLAIR was inferior to PDWI. For lesion/CSF contrast in cavitary lesions, FLAIR was superior to PDWI. There was no significant difference between PDWI and FLAIR for hemorrhagic lesions types 1 and 2. In assessing nonhemorrhagic noncavitary lesions, FLAIR was superior to T2WI for lesion/CSF contrast, but for lesion/WM CNR, FLAIR was inferior to T2WI. In cavitary lesions, T2WI was superior to FLAIR for lesion/WM contrast and CNR. In type 2 hemorrhagic lesions, there was no significant difference between T2WI. CONCLUSION: The FLAIR sequence is more useful than T2WI for the detection of nonhemorrhagic noncavitary lesions, but in the evaluation of cavitary and hemorrhagic lesions, it has limitations. The results suggest that the FLAIR sequence can be used as a complementary imaging sequence, but should not replace the routine T2WI.