© 2015 Wiley Periodicals, Inc. Introduction: The aim of this study was to compare ultrasound echo intensity (EI) with high-resolution T1-weighted MRI and to establish calibration equations to estimate percent intramuscular fat from EI. Methods: Thirty-one participants underwent both ultrasound and MRI testing of 4 muscles: rectus femoris (RF); biceps femoris (BF); tibialis anterior (TA); and medial gastrocnemius (MG). Results: Strong correlations were found between MRI percent fat and muscle EI after correcting for subcutaneous fat thickness (r=0.91 in RF, r=0.80 in BF, r=0.80 in TA, r=0.76 in MG). Three types of calibration equations were established. Conclusions: Muscle ultrasound is a practical and reproducible method that can be used as an imaging technique for examination of percent intramuscular fat. Future ultrasound studies are needed to establish equations for other muscle groups to enhance its use in both research and clinical settings.