Reactive arthritis, also called Reiter's syndrome, is the most common type of inflammatory polyarthritis in young men. It is sometimes the first manifestation of human immunodeficiency virus infection. An HLA-B27 genotype is a predisposing factor in over two thirds of patients with reactive arthritis. The syndrome most frequently follows genitourinary infection with Chlamydia trachomatis, but other organisms have also been implicated. Treatment with doxycycline or its analogs sometimes shortens the course or aborts the onset of the arthritis. Reactive arthritis may also follow enteric infections with some strains of Salmonella or Shigella, but use of antibiotics in these patients has not been shown to be effective. Reactive arthritis should always be considered in young men who present with polyarthritis. Symptoms may persist for long periods and may, in some cases, cause long-term disability. Initial treatment consists of high doses of potent nonsteroidal anti-inflammatory drugs. Patients with large-joint involvement may also benefit from intra-articular corticosteroid injection.