We report a case of a nerve sheath ganglion of the ulnar nerve at the canal
of Guyon. This case involved a ganglion which was confined to the epineuri
um of the ulnar nerve, and it was completely excised without any damage to
the nerve fiber. A nerve-sheath ganglion is rare, but it should be consider
ed in the differential diagnosis of any tumor which is causing neural distu
rbance.