Invasive fungal disease (IFD) causes significant morbidity and mortality among children undergoing allo-SCT. In this prospective pilot study, we analyze voriconazole as primary antifungal prophylaxis. From October 2004 to July 2010, 56 children o18 years of age were enrolled in this study. Patients received voriconazole doses of 5 mg/ kg per 12 h (n ¼ 23) or 7 mg/kg per 12 h (n ¼ 33), with a limiting dose of 200 mg/12 h, from day À1 to day þ 75 or later in patients with active acute GVHD. Patients were followed up for IFD for 6 months. In this series, 37 (66.1%) patients successfully completed treatment (85.7% during neutropenic period) without empirical or preemptive antifungal therapy, adverse effects or IFD. Nine (16.1%) children needed preemptive (n ¼ 2) or empirical (n ¼ 7) antifungal therapy, and one (1.8%) of them developed a fatal probable IFD during the study period. A total of 10 (17.8%) children developed adverse effects related to voriconazole prophylaxis, leading to definitive withdrawal on median day 26.5 (in 7 patients after granulocytic recovery). The most frequent adverse effect was persistent elevation of hepatic enzymes in seven (12.5%) children. There were no differences between doses of 5 and 7 mg/kg per 12 h. Our results suggest that voriconazole can be safely used as primary antifungal prophylaxis in children undergoing allo-SCT.