Anomalous systemic arterial supply to the basal segment of the left lung (ABLL) is a rare congenital disorder in which an aberrant artery arising from the descending thoracic aorta supplies the basal segment of the left lower lobe, which is then drained through the normal pulmonary vein. We report two cases of ABLL treated at Nippon Medical School Chiba Hokusoh Hospital. The first patient was a 56-year-old woman who was admitted to our hospital because of hemoptysis. ABLL was suspected on the basis of computed tomography of the chest. The second patient was a 22-year-old man who was admitted to the emergency room of another hospital presenting with severe hemoptysis due to a contusion of the back, and was then transferred to our hospital after the symptoms improved. ABLL was diagnosed in both patients by means of bronchoscopy and angiography (aortography and pulmonary arteriography). Left lower lobectomy and ligation of aberrant artery were successfully performed.