The aim of this study was to evaluate the evolution of intraarticular disease in posttraumatic shoulder instability. Ninety-one patients with posttraumatic shoulder instability were examined arthroscopically. The intraarticular disease was recorded on a special documentation sheet (containing 67 descriptive items). The patients were divided into 5 subgroups: first-time dislocation (n = 9); first or second recurrence (n = 12); 3 to 5 recurrences (n = 23); 6 or more recurrences (n = 32); and chronic subluxations (n = 15). All data were examined statistically. Each lesion was correlated with stage of evolution, age, and number of recurrences. The most frequent lesions were regrouped into "lesion families." The initial and most constant lesion was the periosteal disinsertion of the anteroinferior labrum (single lesion). The labral detachment was succeeded in a second stage by the disinsertion of the glenohumeral ligament complex (double lesion). With additional recurrences, stress mechanisms altered the detached structures through tissue damage (triple lesion). The fourth stage saw the extension of the degenerative process, which led to failure at the insertion site and destruction of the labrum-ligament complex (quadruple lesion). This study reveals that recurrences progressively damage stabilizing structures. A pathophysiological classification into 4 stages is proposed, however, that would permit a precise therapeutic strategy for arthroscopic shoulder stabilization.