OBJECT: Failed surgical treatment for ulnar neuropathy or neuritis due to dislocation of the ulnar nerve presents diagnostic and therapeutic challenges. The authors of this paper will establish unrecognized dislocation (snapping) of the medial portion of the triceps as a preventable cause of failed ulnar nerve transposition. METHODS: Fifteen patients had persistent, painful snapping at the medial elbow after ulnar nerve transposition, which had been performed for documented ulnar nerve dislocation with or without ulnar neuropathy. The snapping was caused by a previously unrecognized dislocation of the medial portion of triceps over the medial epicondyle. Seven of the 15 patients also had persistent ulnar nerve symptoms. The correct diagnosis of snapping triceps was delayed for an average of 22 months after the initial ulnar nerve transposition. An additional surgical procedure was performed in nine of the 15 cases and, in part, consisted of lateral transposition or excision of the offending snapping medial portion of the triceps. Of the four patients in this group who had persistent neurological symptoms, submuscular transposition was performed in the two with more severe symptoms and treatment of the triceps alone was performed in the two with milder neurological symptoms. Excellent results were achieved in all surgically treated patients. Six patients declined additional surgery and experienced persistent snapping and/or ulnar nerve symptoms. CONCLUSIONS: Failure to recognize that dislocation of both the medial portion of the triceps and the ulnar nerve can exist concurrently may result in persistent snapping, elbow pain, and even ulnar nerve symptoms after a technically successful ulnar nerve transposition.