The aim of this study was to investigate whether, in patients with antiphospholipid syndrome, anticardiolipin antibodies pass from mother to offspring sera and amniotic fluid. Eleven patients with antiphospholipid syndrome (study group) and 11 healthy controls, matched by maternal and gestational age (control group) were prospectively examined for the presence of anticardiolipin antibodies in the cord blood during labour, and amniotic fluid during vaginal or Caesarean delivery. Three neonates (27.3%) in the study group had anticardiolipin antibodies in the cord blood, while none had them in the control group. Anticardiolipin antibodies were detected in the amniotic fluid in six (54.5%) of the study group pregnancies, compared with none in the control group. No adverse neonatal outcome was noted except for significantly lower (P < 0.0006) mean birth weight in the study group. Anticardiolipin antibodies can pass the placenta and be detected in fetal cord blood and amniotic fluid. This finding might be used in the future for the assessment of pregnancies with antiphospholipid syndrome.