To characterize the clinical features of oncology patients presenting with shortness of breath mistakenly diagnosed at first with pulmonary emboli, but later found instead to have extrinsic compression of the pulmonary artery or its tributaries by tumor. Medical charts and computed tomography (CT) angiographies of these patients were reviewed retrospectively. In a 7-year period, 11 patients from a single institute were identified. Five patients were excluded as they had a pleural and pericardial effusion that by itself could result in dyspnea. All had varied solid tumors and none had lymphoma. In three of six patients, an increased ratio between right and left ventricle was detected by CT angiography; however, in contradistinction to patients with pulmonary emboli, this was not found to be associated with short survival. The term 'pseudo pulmonary emboli' is suggested to describe this phenomenon. Anticoagulant treatment to avoid in-situ pulmonary artery thrombosis may be considered; however, misdiagnosis of pulmonary embolism may delay the appropriate treatment with chemotherapy, biological therapy, and radiotherapy.