Background: Accumulating body of evidence suggests a role for the complement system in the etiology of abortion. Objectives: To evaluate levels of complements (C3, C4) in cases of abortion with or without circulating antiphospholipid (APL) and anticardiolipin (ACL) autoantibodies. Patients and Methods: A total of 103 women were enrolled in this case controlled study including 73 patients with a history of three or more abortion and 30 healthy parous women. For all, ACL, APL, C3, C4 levels were estimated. Results: The means and ranges of circulating complements (C3, C4) were as follows [C3 level: (90 ± 9; 39-115 mg/dl versus 109±16;95-138 mg/dl) in patients and controls respectively; C4 level: (18±10; 11-25 mg/dl; versus 36±7; 23-39 mg/dl) in patients and controls respectively]. The differences in the means between patients and controls were highly significant (p ≤ 0.01). In the patients' group, according to the mean, the range of C4, C3 and the elevation of both ACL and APL, three subgroups (A, B, C) were recognizable. Group A included 21 aborting women with high levels of ACL and APL. Their complement levels (mean ± S.D; range) were as follows:[C3: (59.7±11.6; 39-65 mg/dl); C4: (14.7±5.2; 11-16 mg/dl)]. Group B included 34 aborting women with normal levels of ACL & APL. Their complement levels (mean ± S.D, range) were as follows: [C3: (88.6±19.3; 59-90 mg/dl ) and C4:(18.4±7.3; 15-21 mg/dl)]. Group C included 18 aborting women with normal levels of AC & APL and their complement levels (mean ± S.D; range) were as follows:[C3: (102.7± 15.1; 90-115 mg/dl) and C4: (21.4 ± 5.8; 17-25 mg/dl)]. The differences between the means of C3 in these subgroups were highly significant (p < 0.01), while the differences between the means of C4 between B and C were not significant. Conclusion: Low C3 & C4 levels were detected in recurrent aborting women with or without autoantibodies (APL & ACL). These data may suggest a role for these complements in the pathogenesis of recurrent pregnancy loss.