Postinfection arthritis represents a significant portion of the referrals to pediatric rheumatology centers, particularly in the United States. Many viral and common bacterial infections can be associated with arthritis, and their recognition can sometimes be difficult on a clinical basis. In patients with acute onset of arthritis, the clinician should actively seek epidemiologic, clinical, or laboratory evidence of infection. Diagnostic tests should be used rationally and results interpreted carefully. Some infections, once recognized, require antibiotic treatment, but in most cases anti-inflammatory therapy is successful in treating articular symptoms.