The patient was an 18-year-old male. On the left thigh, he had a purplish blue, smooth, and rubbery mass (8×8×4cm) . The lesion was composed of four lobules, and compression produced a bloody discharge. Hematoxylin and eosin staining of a biopsy specimen showed the uniform proliferation of small round tumor cells that had nuclei atypia with loosely arranged chromatin. Scattered mitotic figures were also seen, but there was no rosette formation. Periodic acid-Schiff staining revealed strongly positive granules in the cytoplasm, which were digested by diastase. On immunohistochemical staining, the tumor cells were positive for p30/p32MIC2 and vimentin, but negative for epithelial, neural, and myogenic markers. Cytogenetic studies revealed reciprocal translocation t (10; 11; 22) (p11. 2; q12; q24), and reverse transcriptase polymerase chain reaction demonstrated expression of the chimera gene EWS-FLI 1. General examination revealed no other tumor suggesting Ewing's sarcoma; these results indicated a diagnosis of primary extraosseus Ewing's sarcoma of the skin. [Skin Cancer (Japan) 2003; 18: 320-324]