We report one case of ulnar nerve compression in Guyon's canal due to calcium deposits in a 50-year-old woman with long standing systemic scleroderma. To our knowledge, this is the second known case. The symptoms consisted of a motor and partial sensory disturbance. Calcification of the piso-triquetral joint was prolonging into Guyon's canal, lifting its contents, and into the subcutaneous tissue of the ulnar border of the wrist. Excision of calcium deposits and of the pisiform in combination with external neurolysis of the ulnar nerve resulted in complete relief of symptoms.