The light and electron microscopic features of a sarcomatoid variant of renal cell carcinoma are presented. On light microscopic examination, the initial biopsy specimen showed only a sarcomatoid pattern, but rare transitions to a papillary adenocarcinoma were seen in a few metastatic foci in subsequent autopsy material. However, ultrastructural examination of the biopsy tissue showed complex desmosomal junctions, confirming the epithelial nature of the neoplasm. Complex lateral plications suggested a renal tubular cell origin. We fell that electron microscopic examination of biopsy material in such cases can be of diagnostic value.