We report the case of a 46-year-old man with an uneventful history who was hospitalized for suspected pulmonary embolism. The chest x-ray did not reveal any parenchymatous anomaly but disclosed pseudo-tumoral enlargement of the pulmonary arteries. There was no right ventricular overload at cardiac echography and the pulmonary arterial pressure was normal. Helicoidal angioscan demonstrated aneurismal dilatation of the both pulmonary arteries, complicated by a thrombus on the right. Outcome was favorable with anticoagulation. After ruling out acquired aneurysm, the diagnosis retained was idiopathic aneurysm of the pulmonary arteries.