Parvovirus B19 (B19) causes many clinical disorders, of which the most common are erythema infectiosum, aplastic crisis complicating chronic hemolytic anemia, and hydrops fetalis. In young adults, the skin eruption caused by B19 is accompanied with polyarthritis and polyarthralgia in 60% of the cases. The joint abnormalities predominate in the hands and feet and usually resolve within a week (range 2-21 d). Serological tests show IgM antibodies against B19, confirming the diagnosis of recent infection. Protracted polyarthritis occurs in some patients and seems associated with the DR4 histocompatibility alleles. Rheumatoid factors can be produced transiently in these patients. Other autoantibodies produced in the wake of B19 infection include anti-nuclear antibodies, anti-DNA, anti-SSA/SSB, and anti-phospholipids. Acute B19 infection can simulate early rheumatoid arthritis (RA) or systemic lupus erythematosus (SLE) (lupus-like eruption over the cheeks, cytopenia, etc.). In addition, there have been a few reports of erosive RA or SLE developing shortly after a B19 infection, with positive PCR tests for B19 DNA in synovial tissue or blood cells. Studies in large series indicate that B19 is probably an extremely rare cause of RA or SLE. Vasculitides affecting the small vessels (Henoch-Schonlein purpura, Wegener's granulomatosis), medium-sized vessels (periarteritis nodosa), and large vessels (giant cell arteritis) can occur after B19 infection. Here again, the number of clinical cases is small.