1. In a survey of 107 cases of Erb's paralysis, twenty-seven instances of incipient or actual posterior dislocation of the upper end of the radius were discovered.

2. The type of case in which the dislocation occurs is defined and the early clinical and radiographic signs of the displacement are described and illustrated.

3. The probable causes—muscle imbalance and rigid splinting over a long period—are adumbrated and the prevention and remedies are suggested.

4. The occurrence of anterior dislocation—six cases—and its significance are discussed.