Varicella-zoster virus (VZV) infection was studied in 40 adult patients who underwent cord blood transplantation (CBT) from unrelated donors. Twenty-five patients developed VZV reactivation at a median of 5 months after CBT (range 1.7-26 months). The cumulative incidence of VZV reactivation after CBT was 80% at 30 months. Twenty-two patients developed localized herpes zoster. The remaining three patients developed atypical non-localized herpes zoster, which was associated with visceral dissemination in one patient. All the patients responded well to antiviral therapy. Unexpectedly, the absence of grade II-IV acute graft-versus-host disease (GVHD) was associated with a higher rate of VZV reactivation after CBT (100% versus 55%, P=0.01). These results suggest that recovery of VZV-specific immune responses after CBT is delayed even in patients without severe acute GVHD.