Posterolateral rotatory instability of the elbow is the most common pattern of chronic lateral elbow instability. The primary lesion in posterolateral rotatory instability is injury or attenuation of the lateral ulnar collateral ligament. Posterolateral rotatory instability is diagnosed on the basis of careful history taking and specific physical examination techniques. Reconstruction of the lateral ulnar collateral ligament with repair of the surrounding soft tissue structures is recommended in patients who have symptoms of recurrent lateral instability. Open and arthroscopic reconstruction techniques have resulted in improvement of elbow function and satisfactory results in most patients, although mild limitation in terminal extension of the elbow is a common finding.