PURPOSE: To evaluate the MR imaging findings of patients with mesial temporal sclerosis. MATERIALS AND METHODS:We retrospectively reviewed the MR imaging findings of 116 patients diagnosed by MRI as suffering from mesial temporal sclerosis. In 18 of these, the condition was also histologically proven. RESULTS: Among the 116 patients, volume loss of the hippocampus was found in 95 (81.9%) and signal changes of the hippocampus in 53 (45.7%). Decreased signal intensity in the hippocampus on T1-weighted images was found in 13 (11.2%) and increased signal on T2-weighted images in 50 (43.1%). Signal abnormality in the hip-pocampus on both T1- and T2-weighted images was found in ten, and associated extrahippocampal abnormali-ties, as follows, in 20 (17.2%): atrophy of the fornix (n=10), atrophy of the mammillary body (n=8), atrophy of the amygdala (n=10), atrophy or increased T2 signal intensity of the anterior thalamic nuclei (n=2), atrophy of the cingulate gyrus (n=2), atrophy or increased signal intensity of the anterior temporal lobe (n=8), and cere-bral hemiatrophy (n=4). CONCLUSION: A high T2 signal and atrophy of the hippocampus are the most common and important MRI findings of mesial temporal sclorosis. Other abnormal findings, if any, which may be found in extrahippocampal structures such as the fornix, mammillary body and temporal lobe, should, however, also be carefully observed