A 62-year-old man with left flank pain and hematuria was shown to have a staghorn stone in left renal pelvis. Grossly, renal pelvis and calyces were markedly dilated with cystic and hemorrhagic degeneration and renal parenchyma was atrophied. A tumor-like mass was located in a hemorrhagic cyst of the renal upper pole. This mass consisted of giant cells and stromal cells mimicking a giant cell tumor of bone. This giant cell tumor-like proliferation may represent a response to hemorrhage into a cystic cavity. Recognition of this finding is important to avoid the over-diagnosis of neoplastic lesions.