BACKGROUND Arthroscopy is the established ` gold standard' diagnostic investigation for detection of shoulder disorders. We aimed to compare the diagnostic accuracy of arthroscopy with magnetic resonance arthrography (MRA) for detection of shoulder disorders. METHODS Patients who underwent arthroscopy by a single surgeon and preoperative MRA between February 2011 and March 2012 for shoulder instability were identified. MRAs were reported by experienced musculoskeletal radiologists. Labral tears, anterior labral tears, superior labral anterior posterior (SLAP) lesions, posterior labral tears, rotator-cuff tears (RCTs), osteoarthritis, loose bodies and Hill-Sachs lesions were identified. Sensitivity, specificity, positive predictive value and negative predictive value, positive likelihood ratio and negative likelihood ratio were calculated. RESULTS A total of 194 patients were identified. The sensitivity and specificity for anterior labral tears was 0.60 and 0.92, SLAP lesions was 0.75 and 0.81, posterior labral tears was 0.57 and 0.96, any labral tear was 0.87 and 0.76, Hill-Sachs lesions was 0.91 and 0.91, RCTs was 0.71 and 0.86, osteoarthritis was 0.72 and 0.95, and loose bodies was 0.22 and 0.96, respectively. The positive predictive value and negative predictive value for anterior labral tears were 0.88 and 0.71, SLAP lesions was 0.64 and 0.88, posterior labral tears was 0.74 and 0.45, any labral tear was 0.89 and 0.71, Hill-Sachs lesions was 0.66 and 0.98, RCTs was 0.47 and 0.95, osteoarthritis was 0.70 and 0.95, and loose bodies was 0.27 and 0.95, respectively. CONCLUSIONS MRA has high diagnostic accuracy for labral tears and Hill-Sachs lesions, but whether MRA should be the first-line imaging modality is controversial.