Extraintestinal manifestations of Salmonella infection occur more frequently in immunocompromised patients than in healthy persons. About 25 % present as septic arthritis. Particularly patients with SLE are predisposed. We report a case of a 16-year old girl with systemic lupus erythematosus who developed septic arthritis of the left knee. Delayed diagnosis because of similar symptoms of arthritis due to lupus and purulent arthritis led to a destruction of the joint despite systemic antibiotic treatment. Seven months later an endoprosthesis was implanted with good outcome. Early diagnosis, adequate antibiotic therapy and, if necessary, surgical intervention are essential for successful treatment. In patients with SLE suffering from fever or arthritis it is necessary to think of infections particularly due to salmonella.