The Cord Blood Transplantation Study (COBLT), sponsored by the National Heart, Lung, and Blood Institute, is a phase II multicenter study designed to evaluate the use of cord blood in allogeneic transplantation. In this report, we evaluated the outcomes of cord blood transplantation in 69 patients with lysosomal and peroxisomal storage diseases. Patients with mucopolysaccharidoses I to III, mucolipidoses (ML) II (n = 36), adrenoleukodystrophy (n = 8), metachromatic leukodystrophy (n = 6), Krabbe disease (n = 16), and Tay-Sachs disease (n = 3) were enrolled between August 1999 and June 2004. All patients received the same preparative regimen, graft-versus-host disease (GVHD) prophylaxis, and supportive care. End points included survival, engraftment, GVHD, and toxicity. Sixty-nine patients (64% men; 81% white) with a median age of 1.8 years underwent transplantation with a median cell dose of 8.7 x 10(7)/kg. One-year survival was 72% (95% confidence interval, 61%-83%). The cumulative incidence of neutrophil engraftment by day 42 was 78% (95% confidence interval, 67%-87%) at a median of 25 days. Grade II to IV acute GVHD occurred in 36% of patients. Cord blood donors are readily available for rapid transplantation. Cord blood transplantation should be considered as frontline therapy for young patients with lysosomal and peroxisomal storage diseases.