This review is concentrated on specifically diagnosable viral diseases causing recent onset polyarthritis. A suspicion of viral etiology of arthritis should arise when there are symptoms of infection such as fever, skin manifestations, neurologic signs, or when several cases are occurring at the same time, suggesting an outbreak. In addition to the history and clinical examination, serology is a key element in the diagnosis. Some of these infections are known to occur at certain geographic areas, and the local clinicians are aware of this possibility. HIV and HCV infections occur worldwide, and they should be kept in mind when treating patients with recent-onset arthritis.