Purpose To determine risk factors of umbilical cord blood transplantation (UCBT) for patients with lymphoid malignancies. Patients and Methods We evaluated 104 adult patients (median age, 41 years) who underwent unrelated donor UCBT for lymphoid malignancies. UCB grafts were two-antigen human leukocyte antigen–mismatched in 68%, and were composed of one (n = 78) or two (n = 26) units. Diagnoses were non-Hodgkin's lymphoma (NHL, n = 61), Hodgkin's lymphoma (HL, n = 29), and chronic lymphocytic leukemia (CLL, n = 14), with 87% having advanced disease and 60% having experienced failure with a prior autologous transplant. Sixty-four percent of patients received a reduced-intensity conditioning regimen and 46% low-dose total-body irradiation (TBI). Median follow-up was 18 months. Results Cumulative incidence of neutrophil engraftment was 84% by day 60, with greater engraftment in recipients of higher CD34⁺ kg/cell dose (P = .0004). CI of non–relapse-related mortality (NRM) was 28% at 1 year, with a lower risk in patients treated with low-dose total-body irradiation (TBI; P = .03). Cumulative incidence of relapse or progression was 31% at 1 year, with a lower risk in recipients of double-unit UCBT (P = .03). The probability of progression-free survival (PFS) was 40% at 1 year, with improved survival in those with chemosensitive disease (49% v 34%; P = .03), who received conditioning regimens containing low-dose TBI (60% v 23%; P = .001), and higher nucleated cell dose (49% v 21%; P = .009). Conclusion UCBT is a viable treatment for adults with advanced lymphoid malignancies. Chemosensitive disease, use of low-dose TBI, and higher cell dose were factors associated with significantly better outcome.