BACKGROUND: Nuss et al introduced a less invasive method for inserting a stainless steel bar through the small incision on the lateral chest wall into the pectus excavatum. This study was undertaken to assess the effect of the Nuss operation on lung mechanics, CT-Index and hemodynamics. METHODS: Twenty patients (age 4 to 17 years) with severe pectus excavatum underwent the Nuss operation. CT-Index (the internal transverse distance of the thorax/the vertebral-sternal distance at greatest depression) was evaluated before operation. Lung mechanics (dynamic compliance [Cdyn], static compliance [Cstat] and airway resistance [Raw]), hemodynamic changes (heart rate [HR], systolic blood pressure [SBP], and diastolic blood pressure [DBP]), and gas exchange (arterial oxygen tension [PaO2], arterial carbon dioxide tension [PaCO2], pulse oximeter saturation [SPO2] and end-tidal carbon dioxide tension[PETCO2]) were measured before and after the operation. RESULTS: Cdyn and Cstat decreased significantly (P < 0.05), but Raw did not change. PaCO2 and PETCO2 decreased significantly (P < 0.05), and SBP and DBP increased significantly (P < 0.05) postoperatively. CONCLUSIONS: It is concluded that decreased compliance after the Nuss operation may result from reduced thoracic elastance, not to a change of lung parenchyma.