A patient with an islet cell tumor presented initially with a supra-renal mass that histologically had an extensive clear cell component. Electron microscopic and immunocytochemical findings were essential to prove that the extrapancreatic mass with clear cells was an unusual metastatic manifestation of an islet cell tumor. Both the pancreatic and extrapancreatic tumor cells contained neurosecretory granules and produced vasoactive intestinal polypeptide and substance P. The clear cell morphology was due to the accumulation of lipid and glycogen and cytoplasmic swelling.