MR was performed on 23 formalin-fixed brain specimens of patients 60 years old or older at the time of death. In two of these subjects MR had also been performed in vivo prior to death. Fifteen hyperintense white-matter foci were found on long TR MR images in seven brains. These lesions were correlated with gross and microscopic pathology. Six lesions were infarctions, two were small foci of gliosis or noncavitated infarcts, two were plaques of demyelination, one was a minute brain cyst, and one was a congenital diverticulum of the lateral ventricle; in three foci the abnormality was not found. We identified no MR criteria to distinguish noncystic infarction from either gliosis or demyelination. However, MR was able to distinguish all these lesions from fluid-containing spaces-including cystic infarction, brain cyst, and ventricular diverticulum-since the lesions in the latter group may be isointense relative to CSF in vivo or to fluid in the subarachnoid space in the postmortem fixed state on all pulse sequences. The relationship of a ventricular diverticulum and a brain cyst to the ventricle or subarachnoid space serves as an additional differentiating feature on MR. In cases in which CT was also performed, it revealed corresponding hypodensities in two infarctions, but failed to reveal the foci of gliosis (or noncavital infarction), demyelination, or brain cyst. These data suggest that subtle changes of gliosis and demyelination, presumably from chronic vascular insufficiency, and/or frank infarction account for the majority of hyperintense white-matter lesions seen in MR in elderly patients. Distinguishing among the various lesions is difficult, but subtle differences are present when MR is correlated with histopathology.