A forty-seven-year-old male miner complained of paresthesia over right hypothenar area and ring and little fiugers for 3 months. On physical examination and electromyography, ulnar nerve dysfunction below elbow was noted. Intraoperatively, an anomalous muscle, the epitrochleoanconeus muscle, was found between the triceps muscle and flexor carpi ulnaris muscle, but it was clearly distinguished from them. Resection of the muscle and medial epicondylectomy were performed. The epitrochleoanconeus muscle is an anomalous muscle which arises from the medial epicondyle of the humerus and inserts into the medial border of the olecranon. The reports on ulnar nerve entrapment syndrome by this muscle were rare. On 14 months follow up, the symptoms and signs were improved.