Wolman disease is a rapidly fatal lysosomal storage disease caused by the complete absence of lysosomal acid lipase activity. We report the cure of an infant with Wolman disease following transplantation of unrelated HLA-mismatched umbilical cord blood-derived stem cells. Umbilical cord blood was chosen as the stem-cell source because of its immediate availability and reduced tendency to cause graft-versus-host disease. The transplantation resulted in restoration of normal acid lipase levels before the onset of permanent end-organ damage. Four years after transplantation, the patient is thriving and has normal levels of acid lipase in peripheral blood cells. To our knowledge, this is the first report of a successful unrelated cord blood transplant in a patient with Wolman disease. Umbilical cord stem cells transplantation can restore acid lipase levels in Wolman disease, and if performed early, can cure the disease.