The relative elongation with elbow flexion of the ulnar nerve, proximal and distal to the cubital tunnel, and of the cubital tunnel retinaculum, was measured in cadaver specimens by stereophotogrammetry. The proximal part of the ulnar nerve elongated significantly with full elbow flexion. No significant change of length was measured in the distal part of the nerve. The length of the cubital tunnel retinaculum increased by an average of 45% from full elbow extension to full flexion.