Seventy-two patients undergoing allogeneic transplantation were treated with voriconazole (VOR) as antifungal prophylaxis starting from day -2 of transplantation and continuing until withdrawal of immunosuppression. Patients were assessed for safety and the incidence of definite, probable, or possible fungal infection throughout transplantation was evaluated. VOR was well tolerated. Only 14% of patients required interruption of VOR therapy because of toxicity: liver toxicity (8%), cardiac Q-T interval prolongation (1%), or other side effects (5%). In the early post-transplant period (<120 days), only 2 patients developed invasive fungal infection: 1 mucormycosis infection and 1 disseminated Aspergillus infection. In the late post-transplant period (>120 days), no patients developed probable or definite fungal infection while receiving VOR. No Candida infections were seen in either period. These data suggest that fungal prophylaxis with VOR following allogeneic transplantation is safe and effective.