PURPOSE: The epidermal cyst is a very common skin lesion which usually occurs in the hairy regions. They are generally small but rarely reach more than 5 cm in diameter. We present a patient with a giant epidermal cyst on buttock area. METHODS: A 50-year-old man with a slowly enlarging, huge mass in his left buttock was examined. There was no history of trauma in this area. Physical examination revealed a soft, nontender, 15x15cm-sized mass in his left buttock. T1-weighted magnetic resonance images demonstrated a well-circumscribed, multilocular cystic lesion with homogeneous, slightly high signal intensity. On T2-weighted images the lesion had wide areas of high signal intensity. The mass was totally excised. RESULTS: A histopathological finding revealed that the cystic wall was lined with whole layers of stratified squamous epithelium. Keratin layers from the surface of the epithelium were seen to be sloughing into the cystic lumen. Multinucleted giant cells were found outside the cystic wall. CONCLUSION: Herein we report a rare case of giant epidermal cyst occurring on the buttock.