A pectus index can be derived from dividing the transverse diameter of the chest by the anterior-posterior diameter on a simple CT scan. In a preliminary report, all patients who required operative correction for pectus excavatum had a pectus index greater than 3.25 while matched normal controls were all less than 3.25. A simple CT scan may be a useful adjunct in objective evaluation of children and teenagers for surgery of pectus excavatum.