A congenital aneurysm of the ductus arteriosus Botalli was detected by chest X-ray as an intrathoracic mass in a 7-day-old infant. Following confirmation of the diagnosis by echocardiography and MRI the aneurysm was successfully resected via left lateral thoracotomy without cardiopulmonary bypass. The postoperative course was uneventful. Six years after operation the patient is asymptomatic and growing normally. An intrathoracic mass may be considered in the differential diagnosis especially in infants and children. Aneurysms of ductus arteriosus potentially are associated with serious complications. Timely diagnosis and early surgical intervention are decisive for prevention of serious complication and death.