One case of congenital, multicentric reticulohistiocytoma of the skin was followed up for more than a year. All lesions disappeared within 31/2 months, and there was no recurrence. Electron microscopic examination revealed typical histiocytic proliferation. Characteristically, the majority of the tumor cells contained numerous dense bodies, many of which showed myelin-like laminations. About 10% of the tumor cells contained Langerhans' cell granules. Some of these cells also contained myelinated dense bodies. These features, which are not commonly seen in Langerhans' cells of histiocytosis X, and the benign course of the disease were emphasized as differentiating points of this entity from histiocytosis X. No cell exhibited a resemblance to ganglioneuronal cells.