A 31-year-old man experienced bilateral posterior glenohumeral dislocation during seizures. He had cleidocranial dysplasia with complete absence of both clavicles. Cleidocranial dysplasia is a rare inherited disease also known as Marie-Sainton syndrome and responsible for dental abnormalities well-known to stomatologists and dentists. Other manifestations include defective development of the skull bones and hypoplastic or aplastic clavicles. We found no previous reports of bilateral posterior glenohumeral dislocation in patients with cleidocranial dysplasia. The objective of this work was to look for an association between clavicular aplasia and posterior glenohumeral dislocation.