Background. Bone marrow has been shown to be superior to peripheral blood, as a stem cell source, in young patients (<20 years of age) with acquired aplastic anemia undergoing a matched sibling transplant. The aim of this study was to test whether this was currently true also for older acquired aplastic anemia patients.Design and Methods. We have therefore analyzed 1886 patients, who received a first matched sibling transplant between 1999 and 2009 : patients were selected as having acquired aplastic anemia, a first transplant from an human leukocyte antigen identical sibling, and bone marrow(n=1163) or peripheral blood (PB) (n=723) as a stem cell source.Results. In multivariate COX analysis negative predictors for survival were the following: patient age >20 years (RR 2.0, p<0.0001), an interval diagnosis-transplant (Dx-Tx) >114 days (RR 1.3, p=0.006) , no anti-thymocyte globulin in the conditioning (RR 1.6, p=0.0001), a conditioning regimen other than cyclophosphamide (RR=1.3, p=0.008) and the use of peripheral blood as a stem cell source (RR 1.6, p<0.00001). The survival advantage for bone marrow compared to peripheral blood, was significant in patients aged 1-19 years (90% vs 76% p<0.00001) as well as in patients aged >20 years (74% vs 64%, p=0.001). The advantage for bone marrow over peripheral blood was maintained above the age of 50 years (69% vs 39% p=0.01). Acute and chronic graft vs host disease were more frequent in peripheral blood transplants. Major causes of death were GvHD (2% vs 6% in bone marrow/peripheral blood respectively), infections (6% vs 13%), and rejection (1,5% vs 2,5%).Conclusions. This study shows that bone marrow should be the preferred stem cell source for matched sibling transplants in acquired aplastic anemia, in all age groups.