We are presenting a unique case of a sub-periosteal osteoid osteoma involving coronoid fossa in a 25-year-old male. He was symptomatic for 2 years and his presentation mimicked mono-articular inflammatory arthritis. His plain radiographs were normal and the computed tomogram confirmed features of a sub-periosteal osteoid osteoma. He was treated with arthroscopic excision of the lesion. Pain relief was noticed immediately after the surgery and maintained at latest follow up of 1 year.