We examined the chest CT findings in 12 cases of intralobar pulmonary sequestration. We classified 4 subtypes by evaluating bronchial and alveolar structures, thus: type A (3 cases), mild cylindrical dilatation of the bronchial structure and hyperlucent alveolar structure; type B (3 cases), marked cylindrical dilatation of the bronchial structure and hyperlucent alveolar structure; type C (2 cases), multicystic dilatation of the bronchial structure and alveolar structure without hyperlucency; and type D (4 cases), multicystic dilatation of the bronchial structure and absence of any alveolar structure. All 77 cases (present and previously reported cases) with CT-documented intralobar pulmonary sequestration could be classified into 4 subtypes: type A 9%, type B 34%, type C 19%, and type D 38%. We concluded that these 4 types were useful for the radiological diagnosis of intralobar pulmonary sequestration.