The authors report the case of a 15 day old neonate presenting a beta hemolitic streptococic (group A) infection, followed by cardio-respiratory failure and radiological opacification of the left superior lobe associated with ventilatory troubles at the left lung base. Massive hemoptysis made an angiographic study mandatory with the diagnosis of a mediastinal vascular tumor placed besides the left descending aorta with compression of the left bronchovasculary pedicule. Tumor ressection was not possible during surgical exploration and a left superior lobectomy was performed. Histological examination showed pulmonary infarctus. The child died a few weeks later. Autopsy revealed mycotic arterial aneurysm of the superior bronchic artery, a very rare lesion considering its localisation and the age of the patient.