Graft versus host disease (GVHD) is one of the obstacles encountered in allogeneic bone marrow transplantation (alloBMT) and has a direct impact on the transplant outcome and survival. In this report, we summarized the incidence of acute and chronic GVHD among 71 HLA matched and 9 HLA mismatched sibling alloBMTs performed for various hematological malignancies, mainly leukemias seen at Ibn-i Sina Hospital. Fifty-five were male and 25 were female Turkish patients. Median age was 29 (12-48). Cyclophosphamide(CY)+total body irradiation (TBI)(12), CY+total lymphatic irradiation (TLI)(6), busulfan (BU)+CY(58) and ALG/ATG+CY(4) were the regimens used for conditioning. Cyclosporin A (CsA)+short term methotrexate were given for GVHD prophylaxis except for two syngeneic transplants who both received only CsA. In 22 of the patients ABO and in 30 patients sex mismatched bone marrow was given. Thirty-one (38.8%) patients showed acute GVHD (grade I-II: 22, grade III-IV: 9) and 8 (11.6%) showed chronic GVHD. In HLA matched and mismatched patients acute GVHD incidence were 33.7% and 44.4% respectively. All of the HLA mismatched patients that showed acute GVHD were in advanced stage. Of the patients with acute GVHD, 28 (96.5%) disclosed skin, 22 (75.9%) hepatic and 14 (48.3%) gut involvement. In the chronic form three patients had mild limited, two limited, two moderate and one advanced GVHD. Seven of the patients were lost due to GVHD. To determine the graft versus leukemia effect of alloBMT, we compared the disease free survival (DFS) of the 68 leukemia patients. Although the patients who had grade I-II acute GVHD showed a better DFS than the patients who did not have acute GVHD, it did not reach to a significance (15.9 vs 13.6 months: p = 0.43).