Posterior positional dislocation is a form of atraumatic posterior recurrent dislocation commonly presenting in late teenage years. It has been an observation of ours that patients with posterior positional dislocation may have a small skin dimple, or tether, over the posteromedial deltoid of both shoulders. Fourteen consecutive patients with an established diagnosis of recurrent posterior positional dislocation were taken from our diagnostic database and reviewed along with 14 age- and sex-matched controls. For each patient and control, a diagnostic battery of clinical signs of instability was recorded and a photograph taken of the posterior aspect of the shoulder. The posterior dimple sign was associated with posterior instability with a sensitivity of 67% and a specificity of 92%. The clinical association of a posterior skin dimple and posterior recurrent positional dislocation has not been recognized before. This feature is discussed and the literature is reviewed.