Recurrent thrombosis and pregnancy loss are well-recognized features of the antiphospholipid syndrome. Uncertainty exists, however, as to whether other reported features of the antiphospholipid syndrome such as cardiac valvular vegetations are truly part of this disorder or more reflective of associated systemic lupus erythematosus (SLE). Several recent studies have concluded that patients with antiphospholipid antibodies have a higher risk of developing Libman-Sacks endocarditis. This study was performed to determine whether antiphospholipid antibodies are the only risk factors for cardiac valvular disease in patients with primary antiphospholipid syndrome (PAPS) or SLE. Ten patients with PAPS were matched with 20 patients with SLE and 20 healthy control subjects by sex. All participants were tested for anticardiolipin (aCL) antibodies by means of a standardized enzyme-linked immunosorbent assay technique, and all underwent two-dimensional and color-flow Doppler echocardiography. The echocardiograms were interpreted by two cardiologists blinded to the patients' underlying disease. Sixty percent of the PAPS group had cardiac valvular involvement compared with 40% of the SLE group (p = NS). We conclude that cardiac valvular vegetations are common both in aCL-negative patients with SLE and in patients with PAPS. This suggests that aCL antibodies either play no causative role or are not the only risk factors in the development of cardiac valvular vegetations.