Pulmonary tumor embolism is characterized by the occlusion of pulmonary vessels by tumor clots, which can be found in the proximal arteries (macro-embolism) or the small vessels (micro-embolism). The clinical presentation is mainly a progressive dyspnea associated with pulmonary hypertension and subacute cor pulmonale. The diagnosis is difficult, mostly made post-mortem. It is rarely obtained through a combination of multiple diagnostic tests (chest CT, ventilation-perfusion scanning, pulmonary artery cytology, biopsy). Treatment is based on the one of the underlying cancer. The prognosis is poor, and patients usually die within weeks to months. It is a rare cause of pulmonary hypertension that must be considered even without a prior oncological diagnosis.