In patients at risk for pulmonary emboli, consideration is often given to placement of an inferior vena cava (IVC) filter to prevent propagation of a distal thrombus. However, long-term benefits remain controversial, and deep venous thrombosis and IVC thrombosis may result from the procedure itself. Whether a filter if beneficial or even detrimental in patients with the antiphospholipid syndrome (APS) is unclear. We reviewed clinical outcomes in 2 patients who had IVC filter placement years before the diagnosis of the APS and 1 who had a contraindication to anticoagulation. Recurrent pulmonary emboli were seen despite the presence of the filter. IVC pathology sometimes revealed thrombus both proximal and distal to the IVC filter. Pulmonary emboli in the APS may be secondary to deep venous thrombosis (DVT). They may also occur secondary to a cardiac source or in situ thrombosis in the pulmonary vessels. An IVC filter will not be of benefit if the heart or the lungs are the primary source for the emboli. It may also not protect against propagation of a more distal thrombus if collateral vessels develop around the filter or a thrombus is present on the proximal side of the filter. Recurrence of pulmonary emboli after a filter placement should alert the clinician to the possibility of a hypercoagulable state such as APS. Clinicians need to assess risks and benefits carefully before placing a permanent IVC filter in patients with APS. Whether a temporary or retrievable filter is safer in APS and more effective is unknown at the present time.