Introduction Invasive fungal infection is among the leading causes of morbidity, mortality, and economic burden for patients with acute leukemia after induction of chemotherapy. In the past few decades, the incidence of invasive fungal infection has increased dramatically. Its management has been further complicated by the increasing frequency of infection by non-Aspergillus molds (e.g. Mucorales). Neutropenic patients are at a high risk of developing an invasive mucormycosis with fulminant course and high mortality rate (35-100%). Case Outline We are presenting the case of a 72-year-old male with an acute monoblastic leukemia. The patient was treated during five days with hydroxycarbamide 2 x 500 mg/day, followed by cytarabine 2 x 20 mg/sc over the next 10 days. He developed febrile neutropenia, headache, and edema of the right orbital region of the face. Computed tomography of the sinuses revealed shadow in sinuses with thickening of mucosa of the right paranasal sinuses. Lavage and aspirate from the sinuses revealed Rhizopus oryzae. Mucormycosis was successfully treated with amphotericin B (5 mg/kg/day) followed by ketoconazole (400 mg/day). Two months later the patient died from primary disease. Conclusion In patients with acute leukemia who developed aplasia, febrile neutropenia, and pain in paranasal sinuses, fungal infection should be taken into consideration. New and non-invasive methods for taking samples from sinuses should be standardized in order to establish an early and accurate diagnosis of mucormycosis with the source in paranasal sinuses, and to start early treatment by a proper antifungal drug. Clear communication between physician and mycologist is critical to ensure proper and timely sampling of lavage and aspirate from sinuses and correct specimen processing when mucormycosis is suspected clinically.