To clarify the correlation between the histopathological findings and MR signal intensity of the cyst wall, fifteen cystic metastatic brain tumors of eleven patients were imaged using a 0.5T MR unit just before surgery, and the MRI findings were correlated with the histopathological findings of resected lesions. On T2-weighted images, all cyst walls showed hypointensity. On T1-weighted images, the intensity of the cyst wall could be classified into three groups, compared with the cerebral cortex. Walls with hyperintensity on T1WI(group H; n = 6) consisted of ample tumor cells, blood vessels and connective tissues, suggesting viable tumor cells. Iso-intense walls on T1W1(group I; n = 3)had abundant reactive glial tissues. Hypointense walls on T1W1 (group L; n = 5)revealed hemorrhage and/or hemosicerin in the wall, suggesting hemorrhagic necrosis. Thus a good correlation was demonstrated between the MR signal intensities and histopathological findings of cyst walls of cystic metastatic brain tumors. This may contribute not only to more precise diagnosis on MRI but also to more planning for treatment of cystic brain metastases.