We describe a case of salmonella septic arthritis of the knee in a middle-aged woman with the following predisposing conditions: long-term corticosteroids and microscopic collagenous colitis. The patient presented with enteritis caused by the same strain 3 months before the arthritis. The first series of cultures were negative and the possibility of a chronic carriage of the disease was not suspected initially. The patient was treated with antibiotics and arthroscopic washouts; the corticosteroid treatment was maintained. There was a progressive clinical and microbiological improvement and the patient was discharged 3 weeks later. Salmonella montevideo is a rare form of salmonella and is known to be associated with tropical fishes, reptiles and imported species.