Magnetic Resonance Imaging (MRI) and Ultrasound (US) imaging are both routinely used in the assessment of rotator cuff pathology. Factors influencing the frequency of use of the respective technologies include access to equipment, provider preference, and cost. The purpose of our study was to compare the accuracy of in clinic ultrasound with that of MRI in diagnosing pathology of the rotator cuff in a large sample size with limited exclusionary criteria. 500 patient profiles assessed by each imaging type, MRI and ultrasound, who then proceeded to arthroscopic surgery were gathered and analyzed for interobserver agreement between the image interpretation and the surgical observations. While ultrasound displayed slightly higher sensitivity and specificity ratings in the diagnosis of full tears (0.90 and 0.92 vs. 0.86 and 0.91), MRI had a higher sensitivity (0.87 vs. 0.80) and Ultrasound had a higher specificity (0.86 vs. 0.76) for general cuff damage. The Weighted Kappa Values for both MRI (0.699) and Ultrasound (0.668) both indicate a substantial strength of agreement between the image interpretation and surgical findings. While there was a balanced distribution of errors observed in the MRI category, the most common error made in the Ultrasound assessment was a false negative assessment of a partial tear. The data indicate that in a clinical setting Ultrasound imaging is a cost-effective and accurate alternative to MRI and can be a valuable addition to the diagnostic assessment of rotator cuff injury and pathology.