Endogenous circulating anticoagulants are unusual in children without a congenital factor deficiency. In particular, the lupus anticoagulant has only rarely been reported in children. Despite its functioning in vitro to prolong the partial thromboplastin time, patients more frequently have problems with thrombosis than bleeding, unless there is a coexistent prothrombin deficiency or thrombocytopenia. We report the cases of three children with the lupus anticoagulant. Two children had associated thromboses. One had a thrombosis of the iliofemoral system and the other had a partial Budd-Chiari syndrome, a thrombosis of the deep calf veins and ureteric obstruction. The third child had a concomitant prothrombin deficiency and bleeding after tooth extraction. Associated findings in these patients included a positive antinuclear antibody test in two, a positive anti-DNA antibody test in two, a false-positive VDRL test in two, and an antiphospholipid antibody test in two.