We report a rare case of recurrent atraumatic posterior-inferior dislocation of the shoulder in an eight year old girl. After closed reduction of the locked dislocation and conservative treatment three further dislocations occurred. Because of the recurrence of locked dislocations and functional impairment arthroscopy including partial synovectomy was performed. Postoperative rehabilitation included the use of a brace in handshake position for six weeks and strengthening exercises. Within a clinical followup of 24 months the shoulder remained stable without loss of function but atraumatic posterior-inferior dislocation of the contralateral shoulder occured. The bilateral involvement indicates a predisposing factor, predominantly gross capsular laxity, of this rare form of instability.