Patients are often referred to the genitourinary clinic for screening for urethral infections after a clinical diagnosis of Reiter's syndrome or reactive arthritis. We report a case of reactive polyarthritis in which serological evidence of Yersinia pseudotuberculosis infection was found in the absence of the other common precipitating organisms, such as Chlamydia spp, Klebsiella spp, Shigella spp, Campylobacter spp, or Yersinia enterocolitica.