A review of the anatomy of the interlobar fissures is based on a detailed study of 100 fixed and inflated lung specimens (50 right and 50 left lungs). The upper part of the fissural surface of the right lower lobe almost always faces in a slightly lateral direction and is usually concave; the lower part typically faces laterally but is usually convex. The upper part of the left major fissure also almost always faces laterally and is concave; but unlike the right side, the lower part usually faces medially and is convex. The minor fissure is typically oriented so that the anterior part is lower than the posterior part and the lateral margin is lower than the medial margin. Incompleteness of the fissures (fusion between lobes) is common; this study revealed a 70% incidence of fusion across the upper right major fissure, 47% across the lower right major fissure, 40% across the upper left major fissure, 46% across the lower left major fissure, and 94% across the minor fissure. The fissural complex is a term used to describe the variable anatomic relation of the major and minor fissures. Some comments are offered concerning fissural anatomy relative to collateral air drift, the visualization and position of interlobar fissures on chest radiographs, and the appearance of inferior interlobar fluid on the lateral radiograph.