Arthritis occurs in several age groups, in both acute and chronic forms, and may have adverse effect on patientsÕ life styles. In addition, this may lead to loss of work-days and to permanent sequelae in the affected joints. Early/accurate diagnosis of arthritis and prompt administration of appropriate treatment are extremely important to prevent such complications. In this review, the most common microorganisms causing arthritis and laboratory methods used to differentiate infective from non-infective arthritis are discussed.