BACKGROUND: The typical MRI features of hippocampal sclerosis (HS) are volume loss and increased T2 weighted signal intensity. Hippocampal volumetry and T2 relaxometry are useful quantitative methods for presurgical diagnosis of HS, especially in the cases of mild, bilateral or focal hippocampal atrophies. We investigated the value of a new quantitative method using FLAIR (Fluid Attenuated Inversion Recovery) MR images compared to those of visual inter-pretation and MR volumetry. METHODS: Forty-five patients with mesial temporal lobe epilepsy (TLE) and 21 under-went volumetric MRI (T1-weighted, SPGR, T2 weighted, and FLAIR images). All patients underwent anterior temporal lobectomy with amygdalohippocampectomy., where visual analysis and hippocampal volumetry were performed. The absolute and normalized values of hippocampal FLAIR signal intensity [hippocampal FLAIR intensity/superior frontal FLAIR intensity=Hippocampal-Frontal Signal Intensity Ratio (HFSR)] were obtained from both normal subjects and patients with TLE. RESULTS: The pathology of resected hippocampus showed HS in all patients. Visual interpretation of presurgical MRI failed to lateralize HS in 10 patients (22.2%). Among these 10 patients, the HS was lateralized by HFSR method in seven patients (70%) [Five (50%) by right-to-left difference of HFSR and the other two (20%) by analysis of a longitudinal regional curve of HFSR] while it was further lateralized by hippocampal volumetry in only three. CONCLUSIONS: In presurgical evaluation of patients with TLE, the hippocampal FLAIR signal analysis appeared to be complementary to visual interpretation and MR volumetry.