To describe the incidence, risk factors, and treatment of autoimmune diseases (ADs) occurring after cord blood transplantation (CBT), we analyzed both CBT recipients reported to EUROCORD who had developed at least 1 new AD and those who had not. Fifty-two of 726 reported patients developed at least 1 AD within 212 days (range, 27-4267) after CBT. Cumulative incidence of ADs after CBT was 5.0% +/- 1% at 1 year and 6.6% +/- 1% at 5 years. Patients developing ADs were younger and had more nonmalignant diseases (P < .001). ADs target hematopoietic (autoimmune hemolytic anemia, n = 20; Evans syndrome, n = 9; autoimmune thrombocytopenia, n = 11; and immune neutropenia, n = 1) and other tissues (thyroiditis, n = 3; psoriasis, n = 2; Graves disease, n 1; membranous glomerulonephritis, n = 2; rheumatoid arthritis, n = 1; ulcerative colitis, n = 1; and systemic lupus erythematosus, n = 1). Four patients developed 2 ADs (3 cases of immune thrombocytopenia followed by autoimmune hemolytic anemia and 1 Evans syndrome with rheumatoid arthritis). By multivariate analysis, the main risk factor for developing an AD was nonmalignant disease as an indication for CBT (P = .0001). Hematologic ADs were most often treated with steroids, rituximab, and cyclosporine. With a median follow-up of 26 months (range, 2-91), 6 of 52 patients died as a consequence of ADs. We conclude that CBT may be followed by potentially life-threatening, mainly hematologic ADs.