A series of 63 cases of fatal acute pulmonary thromboembolism (PTE) with available necropsy study was evaluated The diagnosis was established ante mortem in 20 cases (predictive index 31%). The diagnosis was only suspected in 2 of the 16 patients in whom PTE was associated with pneumonia (predictive index 12.5%, p less than 0.01), in 3 of the 26 cases if PTE associated with neoplasia (predictive index 11.5% p less than 0.01) and in 8 of the 41 cases with terminal disease (predictive index 19.5%, p less than 0.01). On the contrary, thrombophlebitis and relapsing PTE had a significative facilitation effect on the diagnosis (predictive indexes 53.3% and 52.6%, respectively; p less than 0.01). It was concluded that the presence of neoplasia, pneumonia or terminal illness make the diagnosis of pulmonary thromboembolism difficult.