OBJECTIVE To highlight the clinical presentation and management of a rare case of oncogenic osteomalacia due to an ethmoid sinus tumour. METHODS We examined the case records of a 55-year-old man who presented with progressive fatigue, weakness and bone pain, and noted the clinical presentation, laboratory investigations, computed tomography findings, operative notes and follow-up details. CONCLUSIONS Oncogenic osteomalacia secondary to a paranasal sinus neoplasm is a rare entity. The causative tumour is often occult and may be missed by routine clinical examination. This case report illustrates the appropriate pattern of evaluation and management to ensure a successful outcome.