Objective. To investigate whether in patients with antiphospholipid syndrome (APS), high positive antibody titers are associated with adverse pregnancy outcome. Design. A retrospective cohort study of prospectively collected data. Setting. Sheba Medical Center, Israel, a tertiary referral center. Population sample. Pregnant women with APS. Methods. Anticardiolipin, a-β2-glycoprotein I antibodies, and lupus anticoagulant were measured before pregnancy. Women were divided into those with antibody titers >four times the upper limit of normal (high positive titer, HPT group), and the rest, into the positive titer (PT) group. All women were treated with daily enoxaparin and aspirin. Main outcome measures. Composite adverse fetal/neonatal outcome, defined as one or more of the following: fetal/neonatal loss, preterm birth ≤32 weeks, and birthweight below than 10th percentile. Composite adverse fetal/neonatal outcome was compared between the HPT and PT groups. Maternal adverse outcomes were also compared. Results. 51 women with APS were followed during 55 pregnancies, 20 in the HPT and 35 in the PT groups. The two groups were similar with regard to previous obstetric and clinical characteristics. Among HPT women, only 7/20 (35%) pregnancies culminated in appropriately grown, live-born infants >32 weeks’ gestation, compared with 27/35 (77%) PT pregnancies. The risk of adverse fetal/neonatal outcome was 5.7 times higher (95%CI 1.9–17.7) for HPT than for PT women. Conclusions. Pregnant women with APS and high positive antiphospholipid antibody titers are a unique and extremely high risk group for adverse fetal/neonatal outcome. Stricter surveillance and possibly additional therapy options should be explored for this patient population.