Approximately 10% of all human pregnancies end in spontaneous abortions. In the majority of such cases the etiology remains unknown, but anticardiolipin antibodies are gaining recognition as potential causes of recurrent miscarriage.The prevalence of anticardiolipin antibody IgG (IgGacl) in 60 pregnant patients with recurrent first trimester abortions and 60 pregnant controls of comparable age with no history of abortion were examined to find a possible relation between IgGacl and spontaneous abortion. The assay for IgGacl was done by Enzyme Linked Immunosorbent Assay (ELISA). Positive test results were considered 'strongly elevated' with IgGacl levels exceeding 36 GPL units. Aspirin (80 mg per day) was prescribed for patients with recurrent first trimester abortion and strongly elevated levels of IgGacl.Strongly elevated levels of IgGacl were detected in a total of 18 patients (30%) with recurrent abortions, and none of the controls (p<0.001). Of all the patients with strongly elevated levels, 16 patients had unexplained abortions and 2 had explicable abortions. The relative risk for strongly elevated IgGacl was 3.78. These 16 patients with unexplained abortions were treated with aspirin, 80 mg per day, and a successful pregnancy outcome was observed in 10 patients, while 2 patients were in the third trimester of pregnancy.IgGacl is strongly associated with first trimester recurrent abortions and increases the risk approximately 4-fold. Aspirin is beneficial in patients with recurrent first trimester abortions and strongly elevated levels of IgGacl.