The minor fissure was studied with thin computed tomographic (CT) sections (2 mm thickness, 3 mm interval) in 50 patients. It showed high density line or area in all patients. In nine patients CT sections were not obtained through the all region of the minor fissure. Of other 41 patients the fissure was complete in 12 (29%), slightly incomplete in 18 (44%), half incomplete in 7 (17%), and considerably incomplete in 4 (10%). The upper surface of the middle lobe appeared to be upwardly convex in all 50 patients. The location of the highest portion of the minor fissure was hilar in 12 (24%) of 50 patients, medial 1 (2%), anterior 0 (0%), lateral 8 (16%), posterior 3 (6%), dorsal 10 (20%), central 12 (24%), others 2 (4%), and indeterminate 2 (4%). The minor fissure was higher medially than laterally in 22 (44%) patients, and higher posteriorly than anteriorly in 40 (80%) patients. The lowest portion of the minor fissure was anterior in 20 (40%) patients, lateral in 4 (8%), and posterior 3 (6%). The anterior vein of the anterior segment of the right upper lobe (V3b) came in contact with the minor fissure in 20 (40%) patients. In 18 (90%) of these 20 patients minor fissure medial to V3b was incomplete partially. Three dimensional reconstruction image of the minor fissure improved understanding of the anatomy. Familiarity with the anatomic detail of the minor fissure and with variations in the relationships of the upper and middle lobes is useful in localization or extension of a lesion.