Over 12% of patients who contract Chikungunya virus infection develop chronic joint symptoms. These symptoms respond only partially to the non-steroidal anti-inflammatory drugs. An open pilot study on the efficacy of chloroquine phosphate was carried out and 10 patients completed 20 weeks of therapy. Both the Ritchie articular index and morning stiffness improved significantly. In the patient's assessment, 7 out of 10 considered their conditions to have improved. On the basis of the doctor's assessment, 5 of the 10 had improved. These results justify further controlled blind trials of chloroquine in chronic Chikungunya arthritis.