PURPOSE: To define the anatomy of apical pleural tenting commonly seen in computed tomography(CT) of the upper posterior thorax. MATERIALS & METHODS: Chest CTs of 393 patients with no pleural disease clinically and radiographically were analyzed. GE-9800 Quick and Toshiba-900S were used, employing the usual contrast enhanced CTtechnique. CT findings of focal pleural tenting on the inner side of the upper posterior thorax(apical pleural tenting) were evalvated and analysed in terms of location and shape. The CT findings were compared with the gross findings of the inner aspect of the posterior cadaveric thorax. RESULTS: Apical pleural tenting was formed by the upper border of the subcostal muscle. It's incidence was 44%(n=171), with bilaterality in 29%(n=49), and unilaterality in 71% of cases(n=122). This tenting was most frequently found between the third rib and the fourth intercostal space(81%), and seen in the outer third(42%) or central third(41%) part of the posterior costalpleura. In fifteen cases(7%), it was directed obliquely and had changed its location from the inner to the centralor the central to the outer part. The shapes of the tenting were classified as follows : type 1(convex innerborder with sharp apex, 62%) ; type 2(convex inner border with broad apex, 23%) ; type 3(undulated contour ofapex, 13%) ; and type 4(two-spike apices, 1%). CONCLUSION: Apical pleura tenting is a normal CT finding probably demonstrated by the upper border of the subcostal muscle. Misdiagnosis of pleural disease can be avoided by recognition of the location and type of this tenting.