Allogeneic hematopoietic stem cell transplantation (HSCT) can prolong life and improve its quality in patients with inherited metabolic diseases. HSCT offers a permanent source of enzyme replacement therapy and also might mediate nonhematopoietic cell regeneration or repair. Unrelated cord blood is an exciting newer graft source for treatment of patients with these fatal disorders, providing increased access to donors and significant clinical efficacy, particularly when transplantation is performed in early stages. Pre-transplant performance status is highly predictive of overall survival.