Temporomandibular joint ankylosis involves fusion of the mandibular condyle to the base of the skull. It is a major clinical problem that affects many patients suffering from facial trauma, infection or systemic disease. The treatment of Temporomandibular joint ankylosis poses a significant challenge because of technical difficulties and a high incidence of recurrence. This report describe a rare case of a 16 year-man with complete inability to open his mouth, diagnosed with unilateral post septic left bony Temporomandibular joint ankylosis. The surgical approach consisted of gap arthroplasty followed by vigorous physiotherapy.