Cubital tunnel syndrome (CuTS) is the second most common nerve compression neuropathy in the upper extremity. Intraneural ganglion cyst (IGC) within the ulnar nerve around the elbow, might present as CuTS. A 51-year-old Chinese man presented with paresthesia at the ulnar two digits of the left hand for one year. He was clinically diagnosed as severe CuTS. Nerve conduction study revealed marked axonal damage of the left ulnar nerve and ultrasonography showed a mass along the ulnar nerve, three centimetres proximal to the medial epicondyle, which was highly suggestive of Schwannoma. The mass was explored by a longitudinal incision. Intraoperatively, multiple cystic lesions were found within the epineurium of the ulnar nerve. Communication was seen between the elbow joint and the cyst. Swellings were partially excised under microscope. Decompression or partial excision of the cyst along with ligation of the articular branch should be the treatment of choice to prevent recurrence in case of IGC.