Initial experience with the use of dynamic sonography of the elbow for diagnosing ulnar nerve dislocation and snapping triceps syndrome is reported. Cases of three consecutive patients who underwent sonographic evaluation of the elbow and subsequent open elbow surgery for symptomatic ulnar nerve dislocation were reviewed. Dynamic sonography of the elbow was used to aid in the accurate diagnosis of and differentiation between ulnar nerve dislocation and snapping of the medial triceps muscle.