Adverse outcome of pregnancy is a potentially dangerous complication of conception and affects 15-20% of pregnancies. According to recent studies increased level of blood antiphospholipids antibodies, if accompanied by predisposing factors, can be an adverse event in human pregnancy. The aim of the present study was to compare the maternal serum levels of anticardiolipin and antiphosphatidyl serine, and partial thromboplastin time between patients with adverse outcome of pregnancy and matched subjects with normal pregnancy. Serum levels of anticardiolipin and antiphosphatidyl serine and activated partial thromboplastin time were measured in 150 women with adverse pregnancy outcome and 150 matched women with normal pregnancy after a gestational age of 10 weeks. Data on maternal age, age of pregnancy, serum levels of anticardiolipin and antiphosphatidyl serine, and activated partial thromboplastin time were collected and compared by Student’s t or χ 2 tests. The age of mothers in the two groups were 25.86±5.90 and 27.09±5.63 years (P=0.67), and the age of pregnancies were 29.34±5.12 and 28.17±7.03 (P=0.1) weeks in the control and patient groups, respectively. Positive levels of serum anticardiolipin and antiphosphatidyl serine antibodies, and activated partial thromboplastin time for the control and patient groups were 14.3% versus 85.7% (P=0.002), 15.2 % versus 84.8 % (P=0.003), and 23.1 % versus 76.9% (P=0.001), respectively. The findings suggest that positive levels of serum antiphospholipids are associated with adverse outcome of pregnancy in the study population.