Background: Shoulder impingement syndrome is the most frequent cause of shoulder pain. Ultrasonography (US) and magnetic resonance imaging (MRI) have pivotal role for diagnosing shoulder impingement and rotator cuff pathologies. There are several advantages of US; being a dynamic form of imaging as compared to the static MRI, it is portable, better tolerated by the patient, less time consuming, less expensive and more readily available. Aim: The aim of this study is to compare the efficacy of US and MRI in diagnosis of shoulder impingement, using MRI as a reference standard. Methods: Thirty patients with clinical diagnosis of subacromial impingement were imaged by both US and MRI in the department of Radiology at Benha University Hospitals. The findings of the 2 modalities were recorded and compered. Results: There was no statistically significant difference found between MRI & US regarding supraspinatus tendon pathology and non-rotator cuff pathology (P> 0.05). US showed a sensitivity, specificity, PPV, NPV and accuracy of 100% for each in diagnosing full thickness tear of supraspinatus tendon using MRI as reference. For partial thickness tears, it showed a sensitivity of 80%, specificity of 95%, PPV of 88.9%, NPV of 90.5 % and accuracy of 90%. Conclusion: US is comparable to MRI in evaluation of shoulder impingement syndrome and rotator cuff tears, particularly more accurate in full thickness tears. Since US is less expensive and more available, with advantage of dynamic real time assessment, it could be used as the first line investigation in patients presenting with shoulder pain.