It is still controversial whether fresh avulsion fractures of the medial or lateral epicondyle of the humerus in adults should be treated conservatively or surgically. We monitored 12 patients to consider treatment selection. The patients were examined for site and size of bone fragment, degree of displacement, dislocation of the elbow joint, method of treatment, and bone union and elbow stability. The treatment results were scored according to the Elbow Assessment Score System, and the scores ranged from 86 to 100 points. The scores did not differ significantly among any of the patients, whether treated conservatively or surgically. Although surgery produces good results, conservative treatment can be selected for patients in whom the maximum diameter of bone fragment is 13 mm or less or the displacement of the bone fragment is 9 mm or less.