We reviewed the 12 elbows of 11 children with traumatic epiphyseal separation of the olecranon processes that was treated between 1984 and 1990. 1. Special preponderance was the left elbow of the 13-year-old male. 7 cases were classifid as Salter-Harris Type I, 4 Type II and 1 Type III. 2. We treated 10 elbows by open reduction and internal fixation. All patients including the operated and the nonoperated were graded as the excellent or good by Weseley's evaluation system of results. 3. In 3 cases of seven Type 1 fractures we observed the interposition of cartilagenous flaps between fracture fragments. We recommend open reduction and internal fixation to prevent cartilagenous interposition for the patients with displaced epiphyseal separation of the olecranon process of the ulna.