Internal gestation of a genetically foreign conceptus challenges the maternal host to circumvent immunological processes that recognize and eliminate nonself molecules. Accordingly, human viviparity involves a wide range of immunological modifications. This review examines the relationship between pregnancy and several autoimmune diseases prevalent in women. Pregnancy is associated with improvement in the clinical signs and symptoms of rheumatoid arthritis in more than 70% of patients. Maternal‐fetal disparity in alleles of HLA‐DRβl, DQα, and DQβ has been reported to be associated with pregnancies characterized by remission or improvement. These observations suggest that presentation of fetal DQα peptides might correct autoimmunity in patients with RA either by induction of maternal‐regulatory T cells, or by affecting the maternal T cell receptor repertoire. In contrast, the course of systemic lupus erythematosus is more variable. Whether flare rates increase during or after pregnancy is unsettled, since individual patient series vary in the characteristics of patients accepted for study and in definitions of flare. Despite a high overall flare rate in some series approaching 60%, recorded flares were usually not severe. Only limited data are available regarding the incidence or outcome for either the mother with scleroderma or her fetus. The extent of diffuse skin disease and systemic involvement, particularly pulmonary, cardiac and renal, may be more important than the duration of the disease; limited disease carries a better prognosis for the mother and fetus. Highly specific autoantibody profiles in the mother (independent of whether she has a clinical disease) are associated with fetal demise and neonatal lupus syndromes, the most serious manifestation of which is isolated congenital heart block. The former is associated with antiphospholipid antibodies and the latter with antibodies directed against SSA/Ro and SSB/La polypeptides. J. Leukoc. Biol. 63: 281–287; 1998.