The antineoplastic effect of allogeneic stem cell transplantation after reduced-intensity conditioning (RIC) relies on the graft-versus-tumour (GvT) reaction. GvT is closely linked to the development of graft-versus-host disease (GvHD). The incidence of acute GvHD after RIC seems lower than after myeloablative conditioning (MAC), whereas the incidence of chronic GvHD after RIC seems similar to after MAC. The results of RIC for acute myeloid leukaemia show a non-relapse mortality of approximately 15% at one year, a relapse incidence of approximately 40% after a median of 4-6 months, translating into overall and disease-free survival rates of 40-60%. The factors associated with improved outcome in most studies are the stage of the disease at transplantation, age and the development of chronic GvHD (and thus GvT). In a recent report, chronic GvHD was the most important factor associated with prolonged survival. Future efforts should be directed at aiming to decrease relapse rates. For this purpose, an adequate identification of high-risk patients, close monitoring of minimal residual disease after the procedure, and the use of antineoplastic drugs or immunotherapy may be of help.