Multisystem Langerhans cell histiocytosis (LCH), which includes Letterer-Siwe disease and some severe cases of Hand-Schuller-Christian disease, is usually seen in infants, most frequently by the age of 2 years. It may be present at birth or occur in the neonatal period. Rare cases occur in adults. Multisystem LCH is an aggressive disease that is characterized by chronicity, recurrences, long-term sequelae and even death. Skin, bone, liver, spleen, bone marrow, lymph nodes, and lungs may be involved. Clinical presentation consists of fever, weight loss, seborrheic skin eruptions on front and back of the trunk and over scalp, cytopenias, hepatosplenomegaly, lymphadenopathy, pulmonary infiltrates, and lytic bone lesions. Complications such as craniofacial lesions of ear, eye, or oral cavity, diabetes insipidus due to involvement of posterior pituitary stalk of hypothalamus, neurodegenerative disease, and hemophagocytic syndrome can occur. Patients may develop recurrent otitis media and mastoiditis. About this image: This underweight 4 y/o boy presented with multiple scalp abscesses and red, scaly rash involving scalp and face of 2 years' duration. There was hepatosplenomegaly and painful cervical lymphadenopathy. Note the irregular protrusion of the eyes (exophthalmos). CT skull revealed multiple lytic lesions. Skin and bone marrow biopsies confirmed the diagnosis of multisystem LCH. Based on the clinical presentation and risk organ involvement, this patient would have been diagnosed in the past as a case of Letterer-Siwe disease. He was treated with systemic chemotherapy. Image courtesy of Dr. Nameer Al-Sudany, Global Skin Atlas; used with permission of Dr. Ian McColl.