We report a case of a tumor of the renal medulla. Tumor cells were cha
racteristic of renomedullary interstitial cells as demonstrated by lig
ht microscopy, immunohistochemistry and electron microscopy. Such mass
es are usually small (less than 0.5 cm.) and incidental. This neoplasm
, however, was 5.0 cm. in diameter. To our knowledge, our case is uniq
ue because of tumor size and because it is the first report of an inte
rstitial cell tumor of the kidney that has been clinically observed an
d surgically excised.