Ununited fractures of the clavicle are rare, and when nonunion occurs the cause should be found. Of 18 cases of nonunion here studied, 4 were in the lateral third of the bone, and nonunion was explained by the rupture of the coracoclavicular ligament. When this ligament is intact, union is generally prompt. The other 14 were in the middle third of the bone, and in 10 of these non-union was ascribed to local tissue damage, stripping of soft parts, loss of valuable bone, inadequate internal fixation, and infection connected with the initial treatment by open operation. Surgical correction of fractures of the middle third must be done with due regard to fixation and with minimal damage to soft parts. Fractures of the lateral third, if complicated by disruption of the acromioclavicular ligament, are best treated by internal fixation.