The clinicopathologic correlations of antiphospholipid antibodies (aPLs) have so far only been examined in case reports and highly selected series. This study assessed the incidence of aPLs in 156 consecutive, unselected autopsies and correlated the pathological findings with the clinical histories. Elevations of aPLs were found in 20.5% of the autopsy population, compared with 9.6% of age- and sex-matched controls and 2% of healthy normal subjects. There was a higher incidence of thromboembolic disease in patients with elevated aPL levels compared with those without, but the histology of thrombi was similar in both groups, with no evidence of vasculitis in the aPL-positive individuals. Patients with transient ischemic attacks and cardiac valve lesions had a high incidence of aPLs, as reported previously. Five cases that fit the designation of primary antiphospolipid antibody syndrome were noted. The study concludes that aPLs are relatively common in a hospital autopsy population and are commonly associated with thromboembolic events, that the thromboemboli are not associated with vasculitis, and that primary aPL syndrome is more common than generally appreciated.