The graft-versus-host disease (GVHD) characteristics of 150 consecutive patients undergoing reduced intensity conditioning allogeneic (allo-RIC) transplants and 88 patients undergoing myeloablative conditioning regimen were analysed. All patients received the same GVHD prophylaxis and peripheral blood stem cells from a human leucocyte antigen identical sibling. The cumulative incidence of acute GVHD (aGVHD) was 67% and 44% in the myeloablative and allo-RIC regimen groups, respectively (P < 0.001), and was 39% vs. 29%, respectively (P = 0.043), for grades 2-4 aGVHD. Only conditioning type (myeloablative versus allo-RIC) significantly influenced the incidence of aGVHD in multivariate analysis: Hazard ratio (HR) = 2.16 [95% confidence interval (CI): 1.52-3.07], P < 0.0001. The cumulative incidence of chronic GVHD (cGVHD) was 63% and 71% among myeloablative and allo-RIC patients respectively (P = 0.084). This trend was because of the higher incidence of limited cGVHD, but not extensive cGVHD among allo-RIC recipients [HR = 3.3 (95% CI: 1.42-8.08), P = 0.0017]. Moreover, among patients who developed cGVHD, the cumulative incidence of limited cGVHD was significantly lower in the myeloablative group than in the allo-RIC group (7% vs. 25%, P = 0.007). Duration of immunosuppression was shorter among allo-RIC patients (35.5% vs. 68.8% required systemic immunosuppression 36 months after transplant, P = 0.028). Although prospective controlled trials are required to further evaluate the effect of the conditioning regimen on GVHD, our results suggest that RIC modifies the incidence and characteristics of both acute and cGVHD after allogeneic transplantation, and decreases the immunosuppression requirements in long-term follow up when compared with myeloablative conditioning.