[Unusual compression of the ulnar nerve caused by a hematic cyst].

Among the various possible causes underlying compressive syndromes of the ulnar nerve at the wrist, classified as "occupational neuritides", we must number the presence of a hematic cyst in Guyon's canal. The authors describe the occurrence of a hematic cyst in the region of the pyramido-unciform joint, with prompt and complete restoration of ulnar nerve function after surgical removal of the cyst.