We evaluated the effect of acute and chronic GVHD on relapse and survival after allogeneic hematopoietic SCT (HSCT) for multiple myeloma using non-myeloablative conditioning (NMA) and reduced-intensity conditioning (RIC). The outcomes of 177 HLA-identical sibling HSCT recipients between 1997 and 2005, following NMA (n=98) or RIC (n=79) were analyzed. In 105 patients, autografting was followed by planned NMA/RIC allogeneic transplantation. The impact of GVHD was assessed as a time-dependent covariate using Cox models. The incidence of acute GVHD (aGVHD; grades I-IV) was 42% (95% confidence interval (CI), 35-49%) and of chronic GVHD (cGVHD) at 5 years was 59% (95% CI, 49-69%), with 70% developing extensive cGVHD. In multivariate analysis, aGVHD (≥ grade I) was associated with an increased risk of TRM (relative risk (RR)=2.42, P=0.016), whereas limited cGVHD significantly decreased the risk of myeloma relapse (RR=0.35, P=0.035) and was associated with superior EFS (RR=0.40, P=0.027). aGVHD had a detrimental effect on survival, especially in those receiving autologous followed by allogeneic HSCT (RR=3.52, P=0.001). The reduction in relapse risk associated with cGVHD is consistent with a beneficial graft-vs-myeloma effect, but this did not translate into a survival advantage.