Indeterminate cell histiocytosis is a rare neoplasm composed of cells with mixed characteristics of Langerhans cells and non‐Langerhans cells. An otherwise healthy, 36‐year‐old woman presented with asymptomatic generalized papules and nodules that had appeared on all four extremities, the trunk, and cheeks in the previous 6 months. The lesions were firm, painless, non‐pruritic, and slightly flesh‐yellow or reddish‐brown in color. Histopathologic, immunohistochemical examination and electron microscopic studies showed characteristic findings of indeterminate cell histiocytosis: diffuse proliferative histiocytes infiltrating the dermis without epidermotropism or atypia; neoplastic cells expressing markers characteristic of both Langerhans cells (CD1a, S‐100) and focal monocytes/macrophages (Factor XIIIa, CD68); and no Birbeck granules within the cytoplasm of the neoplastic cells. Flow cytometry revealed more CD34+ cells in the peripheral blood of the patient than in peripheral blood from a control. Interestingly, the patient responded favorably to psoralen ultraviolet A‐range treatment. Herein, we present this case and review the literature.