Abstract
We present a case of Guyon's canal syndrome caused by a synovial cyst within the left wrist of a 48-year-old female patient. The patient presented pain and paresthesia in the region of the ulnar nerve, with loss of muscle strength and left-hand deformity. Electroneuromyography showed a compression of the ulnar nerve at the wrist level. Surgical decompression of the nerve at Guyon's canal with resection of the cyst was performed. After the surgery, the patient presented an improvement in the pain and paresthesia, as well as an increase in muscle trophism and correction of the deformity.