Contact with rat saliva or faeces can lead to infection with Streptobacillu
s moniliformis and the condition known as 'rat bite fever'. We report a cas
e of septic arthritis of the hip due to this organism following a bite on t
he finger of a 14-year-old boy from a rat for sale in a pet shop. The case
was successfully treated by arthrotomy, drainage and joint lavage followed
by administration of penicillin. Septic arthritis of the hip due to S. moni
liformis has not been previously described and this case highlights a possi
ble danger of keeping rats as pets.