Inveterate elbow dislocations remain common in developing countries. We report the case of a 17-year-old child who consulted us after six months of trauma to the left elbow. Clinical examination revealed a deformed elbow, locked in extension with a mobility sector of 5°. The Mayo Clinic Elbow performance score was sixty-six; the downstream vasculo-nervous examination was normal. The face and profile X-ray of the elbow showed a pure posterolateral elbow dislocation. We used the posterior medial para-tricipital and lateral approach, a first stage of arthrolysis was performed. A complete reduction was achieved by progressive and non-traumatic gentle maneuvers. Intraoperative elbow flexion was less than 80°, indicating a retraction of the triceps muscle, so a Z-lengthening plasty was necessary. This reduction was then fixed with two olecranon-humeral K-wires. At the third week, the plaster cast and K-wires were removed. The patient was subsequently referred to a physical therapist. After a ten-month follow-up, an undistorted and functional elbow with a gain of twenty-one points according to the Mayo Clinic score was obtained. Surgical reduction of a neglected elbow dislocation with triceps lengthening plasty, followed by a codified physical therapy program, results in a remarkable restoration of elbow function and stability.