LETTERER-SIWE disease is a generalized macrophage proliferation which involves all organs that contain a prominent reticuloendothelial component. The disease is extremely rare in the newborn period; review of the literature reveals only three cases diagnosed at birth,1-3although there are several reports of cases who historically had rashes at birth but whose diagnosis of Letterer-Siwe disease was made in later months.4-8This report concerns a full-term male infant whose disease presented at birth and was diagnosed by biopsy during the first 48 hours of life. The baby was treated with vincristine sulfate and corticosteroids with apparent success. Report of a Case A white boy was born at the hospital of the University of Pennsylvania after an uncomplicated 40-week gestation. The birth weight was 3.2 kg (7 lb). The mother, age 22 years, and the father, age 23 years, were in good health. Maternal serologic tests for syphilis were