Intralobar pulmonary sequestration has generally been considered a congenital malformation in which an accessory lung bud develops, is enveloped by normal lung, and retains its systemic arterial supply. Also usually included in the "sequestration spectrum" are aberrant arteries to normal lung with either normal or anomalous venous connection. We reviewed all surgical pathology specimens and autopsies performed at Texas Children's Hospital from 1955 through 1984. There were 15 cases with an aberrant systemic artery to normal or abnormal lung. Nine were cases of structurally normal lung with an aberrant systemic artery, and five were cystic adenomatoid malformations with a systemic artery. In one older child some features of intralobar sequestration were present, but a major bronchial connection was retained. We propose that most intralobar sequestrations represent either cystic adenomatoid malformations that clinically are unrecognized until they become secondarily infected or developmentally normal lung supplied by a systemic artery.