Manifest fungal infection of the middle ear, fungal mastoiditis, is a very rare entity, which is almost exclusively seen in immunocompromised patients. The authors present a case of fungal mastoiditis in a 52-year-old woman without immunocompromise. The patient presented with acutely progressing symptoms of hearing loss and dysequilibrium. Bony fistula of the semicircular canal was noted on CT scans and a marginal perforation of the tympanic membrane was also seen. Her hearing recovered following the surgery, which revealed massive granulations and proliferation of fungi but no cholesteatoma in the mastoid cavity. Fungal infection of the middle ear is rare, but can cause serious complications. The possibility should be considered even in immunocompetent patients.