Olecranon fractures in the adult are a common upper extremity injury. There is still no universally accepted classification of these fractures and no uniformity of treatment. Results stated vary considerably, and support can be found in the literature for any of several forms of operative treatment. A review of the literature on olecranon fractures is presented. A system of classification of these fractures based on lateral roentgenograms is proposed; Type I, IIa, IIb, and III (depending on location in the olecranon). An assessment of the results of treatment of 100 patients with such fractures treated by surgical methods is presented. Open reduction and internal fixation with tension band, screws, plate and screws, or band, plate, and screws can be relied upon for satisfactory end results. Type I fractures can be treated by anatomic reduction and tension band wiring; all Type II fractures by tension band technique; Type III fractures with a plate and screws.