AbstractThe clinical and laboratory experience with the lupus anticoagulant was reviewed in 37 patients. The anticoagulant is thought to act by blocking the activation of prothrombin by the prothrombin activator complex of factors Xa, V, and phospholipid. Although the anticoagulant has been principally associated with diseases of immune origin, 14 of the present patients had disorders not thought to be immune in nature. Eighteen patients underwent twenty‐one operative procedures with only a single episode of excessive bleeding. In the authors' experience, the lupus anticoagulant is a rare cause of bleeding.