Background: Invasive fungal infections (IFIs) are a leading cause of morbidity and death in immunocompromised patients. Data on efficacy and pharmacokinetics of posaconazole in pediatric patients are rare (1 to 5). Herein, we retrospectively analyzed adolescent patients who had received posaconazole as antifungal prophylaxis. Methods: We retrospectively analyzed patients who received posaconazole as primary or secondary antifungal prophylaxis. Results: A total of 34 adolescent patients, 19 men (55.9%) and 15 women (44.1%) with a mean age of 15.8 +/- 2.1 years were included. Twenty-five of 34 (73.5%) patients were on primary and nine of 34 (26.5%) patients were on secondary antifungal prophylaxis. Diagnosis of the patients receiving posaconazole as primary antifungal prophylaxis were acute myeloid leukemia (n=12, 48%), hematopoietic stem cell transplantation (n=7, 28%), acute lymphoblastic leukemia (n=5, 20%), and Fanconi aplastic anemia (n=1, 4%). Five patients (55.6%) with hematopoietic stem cell transplantation, 1 patient with acute myeloid leukemia (11.1%), 1 patient with Fanconi aplastic anemia (11.1%), and 2 (22.2%) patients with chronic granulomatous disease received posaconazole as secondary antifungal prophylaxis. Twelve of 25 (48%) patients receiving posaconazole as primary antifungal prophylaxis were complicated by IFI; 4 of them were proven, 6 probable, and 2 with possible IFI. Three of 9 patients (33.3%) receiving posaconazole as secondary antifungal prophylaxis was complicated by IFI (P=0.29), 2 of them were probable and 1 was possible IFI. Five of 25 patients (20%) receiving posaconazole as primary prophylaxis died because of IFI. Conclusion: Improvement of antifungal prophylaxis in patients with high risk of invasive infections seems clearly necessary, and analyzing serum posaconazole levels and individualizing dosing may be 1 approach to improve outcomes.