['Elderly and medically infirm cancer patients are increasingly offered allogeneic nonmyeloablative hematopoietic cell transplantation (HCT). A better understanding of the impact of health status on HCT outcomes is warranted. Herein, a recently developed HCT-specific comorbidity index (HCT-CI) was compared with a widely acceptable measure of health status, the Karnofsky performance status (KPS).', 'The outcomes of 341 patients were evaluated, conditioned for either related or unrelated HCT by 2-gray (Gy) total body irradiation given alone or combined with fludarabine at a dose of 90 mg/m(2). Comorbidities were assessed retrospectively by the HCT-CI. Performance status before and toxicities after HCT were graded prospectively using the KPS and National Cancer Institute Common Toxicity criteria, respectively.', 'Weak Spearman rank correlations were noted between HCT-CI and KPS and between the 2 measures and age, number of prior chemotherapy regimens, and intervals between diagnosis and HCT (all r < 0.20). High-risk diseases correlated significantly with higher mean HCT-CI scores (P = .009) but not low KPS (P = .37). In multivariate models, the HCT-CI had significantly greater independent predictive power for toxicities (P = .004), nonrelapse mortality (P = .0002), and overall mortality (P = .0002) compared with the KPS (P = .05, .13, and .05, respectively). Using consolidated HCT-CI and KPS scores, patients were stratified into 4 risk groups with 2-year survivals of 68%, 58%, 41%, and 32%, respectively.'] Are hematopoietic cell transplantation-comorbidity index and Karnofsky performance status independent predictors of morbidity and mortality after allogeneic nonmyeloablative hematopoietic cell transplantation?