The prevalence of Aspergillus sinusitis is often underestimated because the vast majority of cases are classified as "unspecified sinusitis". Two possible aetio-pathogenic mechanisms can be involved in the development of this fungal infection. Traditionally, the literature emphasised the "anglophone" hypothesis which is based on the inhalation of spores. More recently, the "french" model, based on oro-sinusal fistula and/or the perforation of the maxillary sinus by root canal-filling material, is believed to explain the majority of cases in our industrialised environments. Still, neither model explains the totality of cases and several remain beyond comprehension. The disease most commonly presents as a chronic bacterial sinusitis. The process can however become invasive, thus resembling malignancy, with eventually a fatal outcome. Doctors and dentists should know the possible danger, presented by zinc-oxide-eugenol-paste in the sinus. Radical surgery is the treatment of choice, since a prolonged conservative approach (antibiotics, corticosteroids) can only worsen the prognosis. This paper discusses different aspects of the disease, and presents 10 cases, observed at the University Hospitals of Paris (France) and Leuven (Belgium).