Thirty-seven shoulders with rotator cuff diagnoses proved at arthrography, arthroscopy, or open surgery were examined prospectively with magnetic resonance (MR) arthrography. T1-weighted MR images were obtained with and without fat suppression after intraarticular injection of gadopentetate dimeglumine. Without fat suppression, overall accuracy was 84%. False-positive full-thickness tears were diagnosed in three patients who were proved to have partial tears. False-negative normal tendons were diagnosed in two patients who had partial tears. The corresponding sensitivity and specificity were 90% and 75%, respectively. With the aid of fat-suppressed imaging, full-thickness and partial cuff tears were identified with 100% sensitivity and specificity. Fat-suppressed images also showed intratendinous contrast material imbibition in three torn cuffs with frayed, friable tendon margins. Fat suppression in MR arthrography is valuable in the differentiation of partial from full-thickness cuff tears and in the detection of small partial tears of the inferior tendon surface.