A punch biopsy specimen showed an ulcerated epidermis with a diffuse dermal infiltrate composed of large, mononuclear, oval cells with amphophilic cytoplasm and reniform nuclei. There was exocytosis of the mononuclear cells. The cells stained positive for CD1a (Figure 3) and S-100 protein and negative for CD68 and cKIT. The results of laboratory investigations, including complete blood cell count with differential, electrolytes, serum urea nitrogen, creatinine, calcium, magnesium, phosphorus, liver function tests, albumin, prothrombin time, partial thromboplastin time, urinalysis, urine osmolality, chest radiograph, and general skeletal survey, were normal or negative. Five months after the initial presentation, the patient's skin lesions spontaneously involuted.