Fetal microchimerism is the study of persisting fetal cells in the motheryears after pregnancy and the purported implications for her health and longevity. Due to the association between pregnancy and autoimmune disease (AID), and the preponderance of these diseases in women, laboratory studies have for years attempted to link microchimeric fetal cells with the onset of AID after pregnancy. This new study gave us the opportunity to examine for the first time if this theory could be proven clinically in a large cohort of women. By examining whether different types of delivery affected the onset of AID, we also aimed to indirectly relate this finding to fetal microchimerism. The results did suggest an association between pregnancy and the risk of subsequent maternal AID, with increased risks noted after caesarean section (CS) and decreased risks after abortion. This is the first epidemiological study on the risk of AID following pregnancy. © 2011 Landes Bioscience.