To compare direct MR arthrography and CT arthrography for the preoperative planning of shoulder anterior instability.47 patients were included in this study. 43 patients with clinical history of anterior GHI or recurrent shoulder pain had no clinical findings of rotator cuff abnormality. They experienced multiple anterior dislocations of the shoulder. No patient showed evidence of multidirectional instability or generalized ligamentous laxity. The remaining 4 patients complained of anterior shoulder instability after anchor repair. All the patients underwent direct CT and MR arthrography. The results of CTA and MRA were compared with results obtained from arthroscopy in each patient to detect the sensitivity and specificity of each modality.The sensitivity and specificity of CTA for bankart lesion are 89.4% and 96.4% respectively and of MRA 94.7% and 96.4%, for Perthes lesion the sensitivity and specificity of CTA are 33.3% and 100% respectively and of MRA 66.6% and 100%, for ALPSA the sensitivity and specificity of CTA are 85.7% and 97.5% respectively and of MRA 100% and 97.5%, for GLAD the sensitivity and specificity of CTA are 80% and 97.6% respectively and of MRA 60% and 97.6%, for SLAP lesion the sensitivity and specificity of CTA are 100% and 100% respectively and of MRA 100% and 100%, for absent or degenerated labrum the sensitivity and specificity of CTA are 100% and 100% respectively and of MRA 66.6% and 97.7%, for post operative recurrent Bankart lesion the sensitivity and specificity of CTA are 100% and 100% respectively and of MRA 50% and 100%, for bony glenoid fracture the sensitivity and specificity of CTA are 100% and 100% respectively and of MRA 66.6% and 97.5%.CTA and MRA were equivalent in demonstrating labro-ligamentous and cartilaginous lesions associated with shoulder instability. CTA was superior in detecting post operative instability and glenoid rim osseous lesions that are known to be a decisional element in the surgical strategy. Hence, CTA may be considered a method of choice in the preoperative evaluation of shoulder anterior instability.