We aim to discuss the clinical presentation, investigations and successful management of frontal sinus cholesteatoma. A 26 year old Caucasian female, otherwise fit and healthy, presented with a 4-month history of swollen right eye and sudden visual impairment. The ophthalmological examination revealed right sided proptosis, diplopia and reduced visual acuity. The colour vision was normal and there was no afferent papillary defect. On nasendoscopy, the nasal cavity was unremarkable apart from some fullness at the area of the right uncinate process. Computerized tomography scan identified a space occupying lesion in the right frontal sinus eroding through the orbital roof and displacing the right globe. There was also extensive bony erosion through the posterior table. The patient underwent right sided endoscopic sinus surgery and fronto-ethmoidectomy via an external approach. Intra-operatively, the right frontal sinus was found to be full of keratin. The histological examination showed sheets of keratinous debris. She made a good post-operative recovery and remained disease free at 3 years follow-up. The frontal sinus cholesteatoma is a rare condition but should be included in the differential diagnosis of a slowly expanding lesion occurring in the frontal sinus.