We evaluated a novel alemtuzumab-based conditioning regimen in hematopoietic stem cell transplantation (HCT) for acquired severe aplastic anemia (SAA). In a multi-center retrospective study, 50 patients were transplanted from matched sibling donors (MSD) (n=21) and unrelated donors, UD (n=29), using fludarabine 30mg/m(2) for 4 days, cyclophosphamide 300mg/m(2) for 4 days and alemtuzumab median total dose of 60mg (range:40-100mg). Median age was 35 years (range 8-62). Overall survival at 2 years was 95% +/-5% for MSD and 83% for UD HCT (p 0.34). Cumulative incidence of graft failure was 9.5% for MSD and 14.5% for UD HCT. Full donor chimerism (FDC) in unfractionated peripheral blood was 42%; no patient achieved CD3 FDC. Acute GVHD was observed in only 13.5% patients (all grade I-II) and only two patients (4%) developed chronic GVHD. A low incidence of viral infections was seen. Factors influencing overall survival were HCT co-morbidity index (92% with score 0-1 vs 42% with score ≥ 2, p<0.001) and age (92% for age < 50 years vs 71% ≥ 50 years, p=0.001). Our data suggests that the use of an alemtuzumab-based HSCT regimen for SAA results in durable engraftment with a low incidence of chronic GVHD.