Allogeneic hemopoietic stem cell transplantation of matched unrelated donors carries an increased risk of graft versus host disease (GvHD) and transplant related mortality (TRM). We introduced ATG Fresenius at median dose of 90 mg/kg body weight as part of the conditioning regimen for prevention of serious GvHD. We compared 48 recipients of mismatched transplants with 170 recipients of an HLA-matched transplant. The mismatches involved one or two loci. The groups differed in age [HLA-matched: 33 years (0,9–61) HLA-mismatched: 21 years (0,9–51)] and graft source, bone marrow versus peripheral blood stem cell (matched 67% bone marrow, mismatched 83% bone marrow). They were comparable in diagnosis, stage of disease and conditioning. Key words: Mismatched unrelated donor, anti-thymocyte-globuline, stem cell transplantation