Early cytomegalovirus (CMV) replication (eCMV) after allogeneic hematopoietic stem cell transplantation (allo-HSCT) has been suggested as an independent factor that reduces leukemia relapse risk. We retrospectively analyzed 74 patients with acute myeloid leukemia (AML) who underwent allo-HSCT between August 2006 and September 2012. All recipients were CMV seropositive. In 52 patients, eCMV occurred at a median of 35 days (range, 11-92) after allo-HSCT. Univariate analysis revealed that the factors associated with a reduction in the 5-year cumulative incidence of relapse (CIR) included the first complete remission status at allo-HSCT, non-adverse cytogenetics and molecular abnormalities, pre-transplant serum ferritin level <1,400 mg/dL, chronic graft-versus-host disease (cGVHD), and eCMV. In sub-group analysis, according to the existence of eCMV and cGVHD, those with both eCMV and cGVHD showed the lowest 5-year CIR (P < 0.003). Patients with both eCMV and cGVHD had the best outcome for leukemia-free survival (LFS) (P < 0.001) and OS (P < 0.001). In the CMV-seropositive population, the presence of eCMV in combination with cGVHD had a significant positive effect on LFS and OS after allo-HSCT. When eCMV preceded cGVHD, the relapse rate after allo-HSCT was significantly reduced in patients with AML. Therefore, we suggest that it is critical to have an immunological understanding of the graft-versus-leukemia effect in this setting.