We describe postpartum onset of systemic lupus erythematosus (SLE) associated with parvovirus B19 infection in a mother presenting with fever, polyarthritis, erythema, and multiorgan involvement. B19 infection was revealed by detection of B19 DNA and IgM antibodies. In addition, our patient showed low CD4+ (384 x 10(6)/l) and CD8+ (213 x 10(6)/l) T cells, high immunoglobulin values (23.77 g/l), hypocomplementemia, thrombocytopenia, leukopenia, and anemia. Her daughter had rash associated with increasingly high B19 IgG levels and transient antinuclear and anti-ds-DNA antibodies, suggesting that both development of SLE and active B19 infection occurred in pregnancy and B19 was transmitted prenatally. A 2 year followup showed persisting polyarthritis in the mother and atopy in the daughter.