Thin-section computed tomographic scans of both lungs in 154 patients, including seven cadavers, with lung cancer (n = 37), diffuse (n = 32) or inflammatory (n = 30) lung disease, other proved or suspected disease (n = 23), or healthy lungs (n = 32) were analyzed to determine the frequency of incomplete interlobar fissure (IIF). An IIF was defined as a discontinuous linear shadow that remained in contact with the chest wall. An IIF was found in 128 of 154 right lungs (83.1%) and 77 of 154 left lungs (50.0%). Some bronchovascular structures crossed or passed through two contiguous lobes in the fused area. The most common bronchovascular structure associated with an IIF was a pulmonary vein; this association was found in 87 right lungs (56.5%) and 20 left lungs (13.0%). An IIF was traversed by a pulmonary artery in only seven right lungs and 13 left lungs or by a bronchus in only three lungs. It is concluded that recognition of an IIF might improve understanding of the spread of pulmonary disease.