Aneurysm of the main pulmonary artery is a rare condition which has been reported in association with various underlying pathologies. Its natural history has not been fully defined, and medical management remains controversial. The authors report the case of a 71-year-old man, who presented in the Emergency Department with left chest pain, cough and dyspnea. Chest X-ray revealed enlargement of the upper mediastinum. Complementary examinations, including a pulmonary angiogram, revealed the presence of a giant pulmonary artery aneurysm. The patient was conservatively managed. He was discharged home in good general condition, to be followed up by CT scan and two-dimensional echocardiography. Two years later, the patient's clinical condition is good, with no signs of vascular deterioration.