A PREVIOUSLY healthy 12-year-old boy was seen with a 4-week history of a gradually worsening right frontal temporal headache. At the point of maximum discomfort, the patient had noticed a fixed soft tissue swelling for 2 weeks. Findings from physical examination revealed a 4 × 6-cm swelling of the right frontal temporal region of the head. Computed tomography and magnetic resonance imaging showed a dumbbellshaped mass involving the right frontal soft tissue at the level of the temporalis muscle with erosion through the bone and intracranial extension (Figure 1). No intradural compression was identified. Craniotomy was performed, revealing a vascular, soft, friable tumor, which was resected. A total body bone scan and chest x-ray film revealed no additional disease. Findings from histologic examination of the tumor showed a mixture of large cells with convoluted nuclear grooves and indentations, multinucleated giant cells, and a mixed inflammatory infiltrate composed of eosinophils, neutrophils, and lymphocytes (Figure 2). An immunohistochemical S100 protein stain was performed (Figure 3). Electron microscopy demonstrated diagnostic features (Figure 4).