Invasive aspergillus rhinosinusitis is a potentially lethal complication of chemotherapy-induced neutropenia in patients with acute leukemia. The majority of cases are caused by Aspergillus flavus. The infection is difficult to diagnose early but should besuspected when a neutropenic patient develops persistent fever without a known source, symptoms of rhinitis or sinusitis, cutaneous findings over the nose or sinuses, symptoms and signs of orbital or cavernous sinus disease, or an ulcerating lesion of the hard palate or gingiva. Careful anterior rhinoscopy followed by computed tomography of the sinus helps establish the diagnosis, which should be confirmed by histologic study and culture of biopsied material. Early treatment with aggressive surgery, high-dose amphotericin B and 5-fluorocytosine, and possibly white blood cell transfusions may produce a cure if the patient's bone marrow recovers. Newer antifungal agents offer promise for prophylaxis and treatment of this infection.