Pulmonary embolism (PE) is a common cause of morbidity and mortality in oncologic patients. Furthermore, PE is an unsuspected finding in many cases. To determine the frequency and embolus burden of PE in a consecutive oncologic patient group including symptomatic as well as incidental and initially unreported events. In a retrospective, single-center study from June 2005 to January 2010 all patients with an oncologic disease (ICD-10 code C00 to C96) that received at least one contrast-enhanced computed tomography (CT) examination of the chest were reviewed. The study group included 3270 patients with 6780 examinations. A validated pulmonary artery obstruction index (Mastora score) was used to assess embolus burden. PE was found in 240 of 3270 (7.3%) oncologic patients. The frequency was highly variable among different malignancies ranging from 0% to 25%. In the present study about half of all PE were unsuspected. The mean embolus burden was significantly higher in symptomatic PE than in unsuspected PE (P <0.001). The risk of developing a PE was 1.5 times higher in patients with metastases compared to patients without metastases (P <0.005). Age and sex had no influence on PE risk and embolus burden. PE is a frequent unsuspected finding in staging examinations: particularly in patients with malignancies of the ovary, brain, and pancreas, and in patients with metastases. Therefore, the status of the pulmonary vasculature should be assessed in every staging examination that includes the chest. The effect of therapeutic actions on PE events and the unsuspected finding of PE in follow-up CT examinations require further prospective studies.