Posterior humeral dislocations often go undetected. Proposed explanations for the delay in diagnosis include failure of the evaluating physician to include the condition in the differential diagnosis, suboptimal radiographic evaluation and interpretation, and coincidental injuries such as fractures that can confound the patient’s presentation. It is imperative that the orthopedic surgeon develop a complete understanding of the nature of this injury and its treatment so that patients who present with this condition can be diagnosed and treated effectively. This article provides a detailed discussion of the classification, pathoanatomy, diagnosis, and treatment of traumatic posterior glenohumeral dislocation.