The objective of this study of patients with habitual abortion (HA), was to determine their autoimmune profile and to try to prevent new abortions using low-dose aspirin for 7 months with prednisone in the first trimester only, or with low-dose aspirin alone. A total of 678 healthy patients with three or more HA were investigated for antiphospholipid antibodies, antinuclear and antithyroid antibodies. Among these patients, 277 pregnant women were treated, 214 were given prednisone and aspirin (161 autoantibody-negative and 53 autoantibody-positive women), and 63 autoantibody-negative women received aspirin alone. Autoantibodies were present in 33.9% of the patients, in 82.6% of them anticardiolipin antibodies were found to be isolated or associated with antiprothrombin, antithyroid, circulating anticoagulant, antinuclear or anti-beta2 glycoprotein 1 antibodies. In autoantibody-negative pregnant women treated by prednisone and aspirin or aspirin alone, the success rate of live births was 90.7% (146 out of 161) and 74.6% (47 out of 63) respectively (P < 0.01). In autoantibody-positive patients treated with prednisone and aspirin the success rate was 84.9% (45 out of 53) (not significant). Prednisone and aspirin seemed to be as efficient in autoantibody-negative or positive women but better than aspirin alone in autoantibody-negative women. A double-blind trial is in progress to confirm these results.