Timeless and lesion-related treatment are important in the different shoulder instabilities in order to get a good functional result. Within the step-by-step programme of diagnostic possibilities the double contrast computerised arthrotomography is particularly indicated in recurrent posttraumatic and habitual dislocations, in subluxations as well as for clarification of causes of postoperative recurrence. Besides the documentation of skeletal changes (Hill-Sachs-lesion, Bankart defect), double-contrast arthro-CT offers the possibility to identify detachments of the joint capsule or labral tears. Between 11/90 and 9/93 we performed 38 double contrast arthro-CTs for recurrent shoulder instabilities. 35 men and 3 women were examined. The mean age of the sportive patients were 29 years. Preoperatively we diagnosed in 21 cases a recurrent posttraumatic, in 7 cases a habitual shoulder instability. Apart from one multidirectional and three posterior instabilities we found two cases of subluxation. In the meantime 24 patients were treated with an open stabilising operation of the shoulder. The operative findings were compared with the results of double contrast arthro-CT. In a total of 38 performed arthro-CTs we found labral tears in 4 cases, 14 labral dissections, and 10 times a complete labral discontinuity. 8 of 9 labrum dissections found intraoperatively were correctly identified on CT. One dissection was not even seen retrospectively on arthro-CT. Six of nine complete labrum discontinuities were seen on arthro-CT, three described as a dissection. All capsular detachments and bony Bankart lesions found on CT were confirmed intraoperatively.(ABSTRACT TRUNCATED AT 250 WORDS)