Background: Acute and invasive fungal sinusitis represent rare diseases which can lead to life threatening complications. Immunosuppressed patients are affected primarily. The expansion of transplantation medicine and the progress in therapy of malignant diseases of the lymphatic system are associated with an increase of opportunistic systemic mycoses. Therefore the otorhinolaryngologist is confronted increasingly with these problems and questions for surgery, especially if the symptom of a periorbital inflammation occurs as a sign for a beginning orbital complication and radiological signs of involvement of the paranasal sinuses exist. Patients: We report exemplary about two immunosuppressed patients with an invasive and fulminant fungal aspergillosis of the paranasal sinuses. In spite of systemic antifungal therapy and surgical intervention, intracranial and systemic complications caused a lethal course. Conclusions: In immunosuppressed patients with clinical and radiological signs for a sinusitis and a periorbital inflammation an invasive fungal sinusitis should be considered. Pathogenic aspergillus species are the most common identified in fungal sinusitis. The disease with often lethal outcome requires a careful and fast diagnostic and therapy as well as interdisciplinary cooperation. If and when limited or extensive surgery should be performed remains, because of the rarity and the lacking experience with this disease, still a controversially discussed issue and depends on several factors: the kind of disease, the immunity, the subtype of invasive fungal sinusitis and the degree of tissue invasion.