Isolated sphenoid fungal sinusitis is a rare and often difficult to diagnose condition as the presenting symptoms are often vague and non-specific. In this series each case has a different clinical presentation with a different causative fungus. Although isolated fungal sphenoid sinusitis is usually seen in immunocompromised individuals, two of the three cases presented were immunocompetent. The fungi were Pseudallescheria boydii, Aspergillus fumigatus and Schizophyllum commune. In order to illustrate the great diversity of clinical signs, each case is individually presented. The characteristic radiological signs and the clinical management of each case are also presented. The danger signs of associated pathology are discussed with particular reference to an associated squamous carcinoma in one case. Surgical options and chemotherapy are discussed. Isolated sphenoid fungal sinusitis is a rare condition that if undiagnosed may result in considerable morbidity and even mortality of patients.