Gram-negative septic arthritis is an uncommon but serious complication of rheumatoid arthritis and is usually mono-articular. The present case is unusual in that a septic polyarthritis due to Bacteroides fragilis developed in nine joints. The organism was grown only in anaerobic synovial fluid and blood cultures. The patient recovered after treatment which included repeated needle aspirations of the joints under anaesthesia and oral metronidazole (Flagyl; Maybaker). Any patient with rheumatoid arthritis who develops an acute flare-up of disease in one or more joints should have these aspirated to exclude the possibility of septic arthritis. Both anaerobic and aerobic cultures of synovial fluid and blood should be done. Prompt antibiotic treatment and joint drainage are the cornerstones of treatment.