Reactive arthritis is an infection-induced systemic illness characterized by an inflammatory synovitis from which no viable microorganisms can be cultured. The paradigm of reactive arthritis is an infectious trigger that occurs in a genetically susceptible individual in whom the immune system continues to be stimulated or "react" to an ongoing or cleared infection, resulting in intermittent exacerbations of a variety of immune-mediated signs and symptoms. Although the terms Reiter's syndrome and reactive arthritis are sometimes used interchangeably, Reiter's syndrome is actually the complete clinical triad of urethritis, conjunctivitis, and arthritis. Some patients will never fulfill all three components of Reiter's triad, however, and although the term incomplete Reiter's syndrome is often used in such cases, the authors believe that the term reactive arthritis should be used, as it is less confusing and is inclusive of any extra-articular manifestations.