Reprinted from THE LANGET. February 2,1991. pp. 260-262 Mortality in hereditary antithrombin-lll def iciency—1830 to 1989 F. R. ROSENDAAL H. HEIJBOER E. BRIET H. R. BÜLLER D. P. M. BRANDJES K. DE BRUIN D. W. HOMMES J. P. VANDENBROUCKE To determine whether antithrombin-lll (AT-III) deficiency leads to an excess mortality, we studied 171 individuals from ten families with a proven hereditary deficiency. 73 were classified äs certainly deficient either by direct measurement of AT-III concentration or by mendelian inheritance patterns. 98 individuals had a high probability (05) of deficiency. The 64 deaths recorded did not exceed those expected for the general population adjusted for age, sex, and calendar period. We suggest that a policy of prophylactic anticoagulation for patients with AT-III deficiency cannot be recommended. Lancet 1991, 337: 260-62 Introduction Hereditary antithrombin-III (AT-III) deficiency is an uncommon autosomal disorder that is associated with a tendency to venous thromboembolism in hcterozygous individuals. 1 · 2 The severity of venous thrombosis ranges from superficial thrombophlebitis to pulmonary embolism but the risk of severe thromboembolism in AT-III deficient individuals is largely unknown. The decision to anticoagulate symptom-free AT-III deficient individuals prophylactically is therefore difficult and a randomised trial of anticoagulant treatment against placebo is unfeasible since the disorder is rare and a long ADDRESSES Departments of Clinical Epidemiology (f R Rosendaal, MD, K de Bruin, BSc. J P Vandenbroucke, MD) and Haematology (E BriSt, MD, F R Rosendaal). University Hospital Leiden; and the Centre for Thrombosis. Haernostasis. and Atherosclerosis Research (H Heijboer, MD. H R Buller, MD, D P M Brandjes, MD, D W Hommes, BSc), Academic Medical Centre, Amsterdam, the Netherlands. Correspondence to Dr F R Rosendaal. Department of Clinical Epidemiology, Leiden University Hospital, Buildmg 1 CO-P, PO Box 9600, 2300 RC Leiden, the Netherlands