Intracapsular or subcondylar fractures are the most common mandibular fractures in children. One of the serious complications of a fracture in childhood is ankylosis. According to the limitation of movement as an end result, ankylosis can also be classified as partial or complete and, regarding the type of the ankylotic tissue, as fibrous, osseous or fibro-osseous.This usually occurs after closed reduction or prolonged immobilisation, or in non-treated cases. The best treatment for posttraumatic ankylosis is prevention but for those patients who have developed ankylosis, surgical correction and aggressive physiotherapy is necessary. Clinical case: a case of fifteen-yearold boy with post-traumatic fibro-osseus ankylosis of the temporomandibular joint (TMJ) is presented. The patient had nontreated intracapsular fracture, where the following fibrous ankylosis was developed. Radiographical investigations included an OPG (orthopantomogram) x-ray, CT and MRI. Partial condylectomie and artroplasty was per formed under the nasotracheal general anaesthesia by means of fiber endoscope. The postoperative results showed signif icant improvement in condylar head movement. Maximal interincisal opening (MIO) was before the teatement 18 mm, after the operation 30 mm and 2 months postoperatively 37 mm. After open surgical treatment and active physiotherapy the patient had significally better functioning of the masticatory system.