A 15-year-old woman presented with a slowly enlarging, tender, right chest wall mass present for 4 months. The review of systems was unremarkable, specifically for fever, malaise, or adenopathy. On examination, she was well developed and well nourished, with a 4.2 × 2.8 cm hyperpigmented and indurated plaque of the medial right breast (Fig. 1). This lesion was oval, pink-brown, and studded with five to eight light-brown papular excrescences measuring 0.3-0.5 mm each. Induration did not extend beyond the clinically visible lesion. Lymphadenopathy was not present. Complete blood count, blood chemistries, urinalysis, and pregnancy test were within normal limits or negative. Initial biopsy revealed extensive histiocytic infiltration replacing the entire dermis, with occasional Touton-type giant cells, in a background of chronic inflammation, suggestive of benign histiocytic lesion, such as histiocytoma or xanthoma. Electron microscopy revealed a histiocytic infiltrate with cells having irregular nuclei, frequent indentations, and prominent nucleoli. The cytoplasm of the histiocytes contained scattered mitochondria, profiles of endoplasmic reticulum, and occasional membrane-bound dense bodies. She did not return for follow-up until 10 months later, as the lesion had become tumorous measuring 7.5 × 10.5 cm (Fig. 2). Repeat biopsy revealed a multinodular dermal and subcutaneous tumor composed of spindle- and stellate-shaped histiocytic cells varying in nuclear size and staining (Fig. 3a, b). The nuclei were plump and hyperchromatic, with a background of perivascular infiltrates of lymphoid cells with an admixture of plasma cells. Necrosis was not seen. Occasional atypical and multinucleated giant cells were seen having phagocytized lymphocytes and neutrophils (emperipolesis) (Fig. 3c). Breast tissue itself was not involved by tumor. Special stains revealed the histiocytic tumor cells to be S-100 and KP-1 reactive, compatible with benign histiocytic neoplasm. The tumor was negative for estrogen and progesterone receptors. The lesion was excised totally and the patient remains in excellent health 2 years after surgery, with no evidence of recurrence.