Fractures of the hook of the hamate are rare injuries. Six new cases are presented; the most usual mechanism is probably a direct blow to the area of the hook. The diagnosis, which can only be made by special roentgenographic techniques is usually missed at the acute phase. Most of the cases are diagnosed when painful non-union, fraying tendinitis of the flexor tendons to the ulnar fingers, ulnar or median nerve deficits appear. The adequate treatment is usually excision of the hook fragment.