To compare antiphospholipid antibodies in deliveries with and without stillbirth using a multicenter, population-based case-control study of stillbirths and live births.Maternal sera were assayed for immunoglobulin (Ig)G and IgM anticardiolipin and anti-β2-glycoprotein-I antibodies. Assays were performed in 582 stillbirth deliveries and 1,547 live birth deliveries.Elevated levels of IgG anticardiolipin and IgG anti-β2-glycoprotein-I antibodies were associated with an approximate threefold increased odds of stillbirth (crude odds ratio [OR] 3.43, 95% confidence interval [CI] 1.79-6.60, 3.8% compared with 1.1% and OR 3.17, 95% CI 1.30-7.72, (1.9% compared with 0.6%, respectively) when all deliveries with stillbirth were compared with all deliveries with live birth. When the subset of stillbirths not associated with fetal anomalies or obstetric complications was compared with term live births, elevated IgG anticardiolipin antibodies were associated with stillbirth (5.0% compared with 1.0%; OR 5.30, 95% CI, 2.39-11.76; IgG anti-β2-glycoprotein-I antibodies (1.9% compared with 0.6%) had an OR of 3.00 (95% CI 1.01-8.90) and IgM anticardiolipin antibodies (6.0% compared with 3.0%) had an OR of 2.03 (95% CI 1.09-3.76). Elevated levels of anticardiolipin and anti-β2-glycoprotein-I antibodies were associated with a threefold to fivefold increased odds of stillbirth.Our data support consideration of testing for antiphospholipid antibodies in cases of otherwise unexplained stillbirth.II.