Retroversion of the glenoid articular plane has not received sufficient attention in palaeopathological studies. Occasionally mentioned in severe forms of osteoarthritis, exceptionally studied in extreme congenital forms isolated or in the context of malformation syndromes and overlooked in cases of minor dysplasia, it is nonetheless a valuable marker for identifying debilitating pathological conditions, abnormal shoulder laxity or sequelae of obstetric palsy. It is sometimes associated with other anomalies of the shoulder, the acromion or the coracoid processes of the scapula or the proximal end of the humerus. In this contribution, we first define a new method for measuring glenoid retroversion based on recent embryological and anatomical findings. This new method is particularly well adapted to archaeological remains for its simplicity and the possibility of using it with very fragmentary scapulae. We then applied it to eight pathological cases of various origins, dysplasias or acquired forms of glenoid retroversion; semiological analysis enabled the definition of diagnostic criteria for the main aetiologies. Several new diagnostic features are described, in particular for sequelae of obstetric palsy in adults.