The first case of Clostridium difficile toxin-induced reactive arthritis in a patient with chronic Reiter's syndrome is described and compared with previous cases of reactive arthritis associated with this organism. This case demonstrates how distinct clinical manifestations may develop at different times in Reiter's syndrome, according to the infecting organism. Diagnostic terminology is discussed in this context. Clostridium difficile should now be considered a firmly established cause of reactive arthritis.