Introduction. The odontogenic keratocyst (KO) is classified as a developmental odontogenic cyst, located in the oro-maxillo-facial region with a frequency of 10% of the maxillary cysts. It has aggressive behaviour and a high recurrence rate. The asymptomatic evolution favours the increasing into considerable dimensions, so patients are turning to specialists in the late phases of the disease. The high recurrence rate of KO and its morphopathological features can cause severe complications. Early diagnosis is still difficult to establish due to the particularities of its evolution, the lack of patient’s information and sometimes superficial examination. Case presentation. The patient, IM, m/51 years old, was hospitalised at the Emergency Hospital in the OMF Surgery Department with the diagnosis of Keratocyst in the region of the left mandible branch during 25 to 28 October of 2017, based on the clinical and paraclinical examination: OPG, CBCT. The patient's treatment included preoperative planning, spotting the edges of the cyst with respect to neighbouring anatomical formations, marking osteotomy landmarks, reconstructing the osteotomy segment by adapting and positioning the Titan artificial condyle reconstructive plate. The surgery was performed under general anaesthesia, by external approach: the incision itself, the acute and blunt preparation until the exposure of the mandibular branch with the formation, was performed: block resection with disarticulation of the condyle and mandibular branch, arthroplasty with reconstructive plaque and artificial condyle from „Titan”. Hemostatic control followed, suturing and application of blade-type drainage. The operative piece was sent for morphopathological analysis. Block resection with disarticulation of the condyle and mandibular branch, arthroplasty with reconstructive plaque and artificial condyle from Titan. Discussion. Histopathological analysis confirmed the primary diagnosis. The postoperative period was typical. Complications were not determined post-treatment. The degree of opening of the mouth was 3-4 cm postoperatively, the movements of the jaw free, painless. The radiological examination revealed a restoration of the continuity of the mandible. The patient was monitored immediately postoperatively and dynamically at regular annual follow-up visits for 5 years. Patients diagnosed with KO are of interest due to its localization in areas of vital anatomical importance and slow asymptomatic evolution. The treatment tactic is influenced by the evolution phase and the size of the formation. In the case of small unilocular KO, the surgical treatment is less invasive, while in large multilocular forms the intraoperative trauma increases, which can lead to harmful consequences and complications for the patient. Conclusion. Early diagnosis and early addressing to a specialist will prevent patients from radical laborious interventions and possible complications.