BACKGROUND A case history of a patient with ankylosing spondylitis and peripheral arthritis unresponsive to the conventional drug therapy, but successfully controlled by the use of cyclosporin. METHODS In a 68 years old female patient with a 36 years history of typical ankylosing spondylitis a peripheral polyarthritis (hands, feet, wrists, and knees) developed. The patient did not suffer any other disease known to cause secondary spondylitis (psoriasis, inflammatory, bowel, disease). After the unsuccessful use of non-steroidal antiinflammatory drugs a combination therapy with cyclosporin (4 mg/kg/day) and azapropazone (300 mg t.i.d.) was introduced. RESULTS Clinical improvement was achieved after 6 months of combined therapy, the polyarthritis completely resolved after one year. Therefore cyclosporin was discontinued. After one year the polyarthritis reappeared therefore the cyclosporin therapy was reinstituted with success. CONCLUSIONS Cyclosporin has proved consistently effective in our case to control the peripheral arthritis associated with ankylosing spondylitis.