Stability of the elbow is provided by the congruous nature of the bony articulations and the medial and lateral collateral ligament complexes. The medial ligament provides additional support to valgus stress. The lateral ligament prevents rotational instability between the distal humerus and the proximal radius and ulna. Collateral ligament insufficiency typically is posttraumatic and can occur on either side of the joint. An understanding of the normal anatomy is required to make the correct diagnosis and complete a successful surgical reconstruction.