The purpose this study was to provide an understanding of the location of the extensor carpi radialis brevis (ECRB) and its relationship to surgically relevant landmarks. In part I, 20 fresh-frozen cadaveric elbows were dissected, and the anatomic boundaries of the ECRB origin were determined, including its relationship to the extensor carpi radialis longus, the extensor digitorum communis, the lateral epicondyle, the radiocapitellar joint, the lateral collateral ligament, and the elbow capsule. All measurements were made by 3 separate investigators. Whereas the ECRB and extensor digitorum communis converged distal to the radiocapitellar joint, the bony origin of the ECRB was reliably identified beneath the distal-most aspect of the supracondylar ridge, with a mean dimension of 13 +/- 2 mm in length by 7 +/- 2 mm in width. Part II was performed on 10 separate specimens to document whether the ECRB tendon could be identified and released arthroscopically. In all specimens, the ECRB origin was safely and completely released, by use of the landmarks defined in part I. When the ECRB is released arthroscopically, the elbow capsule must be resected and the tendinous origin of the ECRB released from the top of the capitellum to the midline of the radiocapitellar joint.