In 12 osteoligamentous autopsy elbow preparations, the stability of the elbow was independent of the collateral ligament with flexion of less than 20 degrees and greater than 120 degrees. The anterior part of the collateral medial ligament was the prime stabilizer of the elbow in this range of motion, i.e., the flexion range of function. The maximum valgus and internal rotatory instability after transection of the medial collateral ligament, 20.2 degrees and 21.0 degrees, respectively, were found at elbow flexions from 60 degrees to 70 degrees. Selective repair or reconstruction of the anterior part of the elbow medial collateral ligament may prove to be effective in the treatment of acute or chronic elbow instability.