Peripheral nerve tumors are rare, but schwannoma(neurilemmoma) is the most common peripheral nerve tumor. Schwannomas are well- encapsulat ed lesions, surrounded by a true capsule of epineurium. They have been confused with ganglion or neurofibroma or other soft tissue tumors during pre- operation diagnosis. We experienced 13 patient s (20 cases) who had schwannomas in the upper extremities. They originated from almost all kinds of peripheral nerves of the upper extremities, but mainly from the ulnar nerve (8 cases), one of which also exacerbated to Guyon's canal syndrome. Their symptoms and signs were tingling sensation in 7 cases (54%), local tenderness in 5 cases (38%) and one positive Tinel ' s sign, which were all non- specific. They can displace nerve fibers and must be dissected with caution not to damage the nerve fiber. Magnetic Resonnance Imaging (MRI) or ultrasonogram is helpful t o determine the anat omic position and which peripheral nerve is connected t o the mass. We experienced 2 complicated cases, one of which was one mot or weakness of the 2nd and 3rd extensor digitorum in the radial nerve and the other sensory deficit in the median nerve after excision of the schwannomas. Even if careful dissection of the tumor mass has been performed from the main nerve, transient incomplet e nerve palsy is inevitable.