INTRODUCTION: Fungus ball (FB) represents a granulomatous mass due to a fungal colonization which may disseminate and potentially lead to a systemic infection. Maxillary fungus ball is considered to be a complication of dental treatment and, according to relevant literature, it often stems from improper endodontic therapies. MATERIAL AND METHODS: The authors report the case of a 69-year-old caucasian woman with nasal respiratory distress and frequent sinusitis symptoms. According to clinical and radiological evidence, FESS surgery was planned, thus validating FB diagnostic hypothesis. CONCLUSIONS: Fungal infection should always be considered in patients with sinusitis and previous root canal theraphy. Misdiagnosis can lead to severe complications. Surgical removal seems to be effective and resolutive.