Reiter's syndrome is a condition in which a bacterial infection causes inflammation in a joint (arthritis,) in the lining of the eyes (conjunctivitis) and in the urinary tract (urethritis). Some patients may experience skin and mouth lesions as well.

Reiter's syndrome is a type of reactive arthritis, meaning that an infection elsewhere causes inflammation in a joint or joints. Reactive arthritis is similar to infectious arthritis, where an infection directly invades and inflames a joint.

Infections in the gastrointestinal or urogenital systems can trigger Reiter's syndrome. This initial infection may or may not produce symptoms. Several days or weeks later, the infection can cause inflammation in the areas affected by Reiter's syndrome. It may inflame joints in the knee, foot, ankle, hips and lower back, causing pain, swelling or stiffness.

The conjunctiva, the membrane that lines the eye and inside of the eyelid, may become red and inflamed in one or both eyes. The cervix (mouth of the uterus in women) and urethra (in men and women) may become inflamed and cause urgency or burning during urination. Men, women and children may all come into contact with bacterial agents that trigger Reiter's syndrome.

Joint pain caused by Reiter's syndrome is most common in the legs, spine or hands. Reiter's syndrome belongs to a family of diseases known as spondylarthropathies that attack the spine. These diseases include psoriatic arthritis, ankylosing spondylitis and enteropathic arthritis (arthritis related to digestive disorders such as inflammatory bowel disease or celiac disease).

Reiter's syndrome is an uncommon form of arthritis. Other forms of reactive arthritis may also cause joint inflammation triggered by an infection but may not involve the eyes or genitals. Reiter's syndrome can occur in adults and children. Among adults, it is much more common in men than women.

Most people will recover from the initial symptoms after treatment, although some mild arthritis symptoms may remain for up to 12 months. Some patients experience recurrence of symptoms, which may be due to reinfection. A small percentage of patients may develop chronic, severe arthritis that is difficult to control, according to the National Institutes of Health. The frequency is estimated at 3.5 cases per 100,000.

Reiter's syndrome was first described in 1916 when arthritis, urethritis and conjunctivitis were identified in one patient by Hans Reiter, a German military physician later convicted of Nazi war crimes.