The ulnar nerve entrapment at the wrist is usually caused by carpal ganglion, occupational neuritis, ulnar artery disease, fractures of the carpal bones, tumors, rheumatioid arthritis, etc. The ganglion is the most common cause of the distal ulnar nerve entrapment. A fort-two years old woman complained of insidious motor weakness of the left hand. The electromyogram revealed distal ulnar nerve palsy. On examination, her sensibility of affected hand was normal; there were no Tinel's sign and palpable mass on the Guyon's canal and palm; there was obvious wasting of all the interossei. On surgical exploration, the deep branch of the ulnar nerve was compressed by a ganglion at the mid-palmar space, not in the Guyon's canal. Four months after removal, the clawing of the 4th and 5th fingers disappeared, and the pinch power of the left hand recovered normally seventeen months later.