Reactive arthritis (ReA) develops after an infection elsewhere in the body, generally in the genitourinary or intestinal tract. Chlamydia trachomatis, Yersinia enterocolitica, salmonella, shigella, and campylobacter are frequent triggering agents. Between 60% and 90% of patients are positive for HLA-B27. The arthritis occurs within 4 weeks of the primary infection and is oligoarticular and asymmetric. Extra-articular manifestations include mucocutaneous symptoms, ocular inflammation, and urethritis. The average duration of arthritis is 4 to 5 months but two-thirds of patients have symptoms for more than a year. Bacterial antigens have been found in synovial specimens from patients with ReA, but cultures are sterile. The treatment of ReA comprises non-steroidal anti-inflammatory drugs, intra-articular steroid injections, and physical treatment. Short-term antibiotic treatment has no effect in manifest ReA, whereas a tendency to improvement has been seen with treatment over months, at least after chlamydia infection.