Seven hundred fifty four consecutive cases of pulmonary embolism, diagnosed between 1969 and 1982 at S. Chiara Hospital in Pisa, were examined in order to assess the causes and the rate of the early mortality. Full documentation was not obtained in 47 cases (6.2%) and they were excluded from the study; 81 (11.4%) of the remaining 707 died within 30 days of diagnosis, and in 56.8% of them pulmonary embolism was the primary cause of death. The survival rate was 90.6% in patients with apparently primary pulmonary embolism, 89.8% in post surgical cases, 81.5% in cardiac patients and 75% in patients affected by neoplasm. Twenty five per cent of patients were not treated during the acute phase, because the diagnosis was made more than one month after the onset of symptoms or because the fear of bleeding precluded anticoagulant treatment. The incidence of fatal haemorrhage during treatment was 0.5% overall, and 0.4% in surgical patients. Mortality was 9.2% in patients who received treatment, versus 25.2% in untreated patients. Sixteen fatal recurrent embolisms occurred after the end of treatment: 11 were observed in patients not treated with oral anticoagulants. Routine autoptic examinations, performed in 44.4% of the cases, often demonstrated both recent and organized emboli, especially in cardiac patients. Recurrence of pulmonary embolism may account for both the severity of clinical patterns and the high mortality rate in the early phase of treatment.