OBJECTIVE: This study attempted to determine the relative stabilizing effect of the capsuloligamentous structures to inferior humeral displacement. DESIGN: This was an in vitro study, utilizing cadaveric shoulder specimens. BACKGROUND: Inferior glenohumeral instability has come under increasingly close scrutiny in the literature in recent years, yet a description of the precise pathoanatomy is still lacking. METHODS: Thirteen shoulder specimens were cleaned of soft tissue superficial to the vented joint capsule. The position of the humeral head relative to the glenoid was determined. The humeri were subjected to an inferior load. Static position recordings were obtained for each specimen: (1) with the humerus adducted and abducted, (2) before and after sectioning the superior and inferior capsuloligamentous structures. These recordings were analyzed. RESULTS: In adduction, the humeral head migrated inferiorly as the capsuloligamentous structures were sectioned, but no capsuloligamentous structure was seen to be most important. In abduction, when the inferior capsuloligamentous structures were sectioned first, the humeral head migrated inferiorly (P<0.001). When the superior structures were sectioned first, the humeral head position did not significantly change. CONCLUSIONS: In this experimental model, the inferior capsuloligamentous structures are the primary inferior stabilizers of the abducted shoulder. The primary stabilizers of the adducted shoulder remain unclear.