['We compared the length of costal cartilage and rib between patients with symmetric pectus carinatum and controls without anterior chest wall protrusion, using a 3-dimensional (3D) computed tomography (CT) to evaluate whether the overgrowth of costal cartilage exists in patients with pectus carinatum.', 'Twenty-six patients with symmetric pectus carinatum and matched twenty-six controls without chest wall protrusion were enrolled. We measured the full lengths of the 4th-6th ribs and costal cartilages using 3-D volume rendering CT images and the curved multiplanar reformatted (MPR) techniques. The lengths of ribs and costal cartilages, the summation of rib and costal cartilage lengths, and the costal index [length of cartilage/length of rib * 100 (%)] were compared between the patients group and the control group at 4th-6th levels.', 'The lengths of costal cartilage in patient group were significantly longer than those of control group at 4th, 5th and 6th rib level. The lengths of ribs in patient group were significantly shorter than those of control group at 4th, 5th and 6th rib level. The summations of rib and costal cartilage lengths were not longer in patients group than in control group. The costal indices were significantly larger in patients group than in control groups at 4th, 5th and 6th rib level.'] Does the etiology of pectus carinatum involve overgrowth of costal cartilage and undergrowth of ribs?