Increasing evidence suggests that patients with asthma have activated coagulation within the airways. Whether this leads to an increase in venous thromboembolic events is unknown. We therefore assessed the incidence of venous thromboembolic events in patients with mild-to-moderate and severe asthma as compared with an age- and sex-matched reference population. 648 patients with asthma (283 with severe and 365 patients with mild-to-moderate asthma) visiting three Dutch outpatient asthma clinics were studied. All patients completed a questionnaire about a diagnosis of deep vein thrombosis and pulmonary embolism in the past, their risk factors, history of asthma and medication use. All venous thromboembolic events were objectively verified. In total, 35 venous thromboembolic events (16 deep vein thrombosis and 19 pulmonary embolism) occurred at a median age of 39 (range 20-63) years. The incidence of pulmonary embolism in patients with severe asthma was 0.93 (95% CI 0.42-1.44) per 1000 person-years, 0.33 (95% CI 0.07-0.60) in mild-to-moderate asthma and 0.18 (95% CI 0.03-0.33) in the general population, respectively. Severe asthma and oral corticosteroid use were independent risk factors of pulmonary embolism (hazard ratios 3.33 (1.16-9.93) and 2.82 (1.09-7.30), respectively). Asthma was not associated with deep vein thrombosis. Severe asthma greatly enhances the risk of pulmonary embolism, particularly if chronic corticosteroids are used.