Pulmonary sequestration Is an unusual congenital malformation characterized by the presence of nonfunctioning lung tissue which usually has no communication with the normal bronchial tree and which receives its blood supply from an anomalous systemic artery instead of a pulmonary arterial branch. Two forms of pulmonary sequestration occur: Intralobar sequestration, in which the abnormal pulmonary tissue is incorporated within the normal lung and shares a common covering of visceral pleura, and extralobar sequestration, in which the abnormal pulmonary tissue is separated from the normal lung and has its own pleural investment. Since 1970, five cases of pulmonary sequestration were operated at the Department of Thoracic and Cardiovascular Surgery, College of Medicine, Seoul National University. 1. Among five cues, one was male and the others were female. 2. All were intralobar type and involved left lower lobe. 3. There was no operative mortality following left lower lobectomy and ligation of the aberrant artery.[KTCS 1982;1:27-34]