To examine whether primary hypercoagulable states, such as protein C and protein S deficiencies and antiphospholipid antibody, are associated with an increased risk, severity and recurrence of acute pulmonary thromboembolism, the blood levels of antithrombin III, protein C, protein S, lupus anticoagulant, anticardiolipin antibodies were measured in 23 patients with acute pulmonary thromboembolism, 7 men and 16 women (mean age +/- SD, 52 +/- 5 years), admitted to Nippon Medical School Hospital from January, 1990 through December, 1997. Four patients (17.4%) had protein C deficiency, one had protein S deficiency (4.3%), 10 had lupus anticoagulant (43.5%), and 2 had anticardiolipin antibodies (8.7%). Hemodynamic evaluation by Swan-Ganz catheter and venography of the lower extremity to detect deep venous thrombi were carried out in 20 and 21 patients, respectively. There were no differences between the patients with and without primary hypercoagulable states in age (52 +/- 14 vs 52 +/- 19 years), gender, or percentage of patients with deep venous thrombi in the lower extremity (91.7% vs 88.9%). Mean pulmonary arterial pressure (38 +/- 9 vs 26 +/- 4 mmHg, p < 0.05) and total pulmonary vascular resistance (10 +/- 5 vs 6 +/- 2 Wood unit, p < 0.1) were higher in the 13 patients with primary hypercoagulable states compared with the 10 patients without primary hypercoagulable states. Recurrence of pulmonary thromboembolism tended to be higher in the 13 patients with primary hypercoagulable states compared with the 10 patients without primary hypercoagulable states (46.2% vs 10.0%, p < 0.1). These findings suggest that primary hypercoagulable states, such as protein C and S deficiencies and antiphospholipid antibody, are associated with the severity and increased risk and recurrence of acute pulmonary thromboembolism.