The mortality rate of infants with congenital diaphragmatic hernia (CDH) remains high, despite clinical improvements. Many attempts have been made to find accurate and reliable predictors of outcome. Deadspace (Vd/Vt) and dynamic compliance (DC) measured by single breath CO2 analysis may be useful to evaluate pulmonary function and perfusion. In the present study we analyse both parameters in patients with CDH. Nine patients with CDH were included for Vd/Vt and DC study. Measurements of arterial blood gases (pH, PO2, pCO2) were obtained, oxygenation index and alveolo-arterial difference calculated at diagnosis, preoperatively and postoperatively. Vd/Vt and DC were measured at the same moments by analysis of the CO2 espirogram. Statistical analysis was performed using Fisher exact test, ANOVA and Mann Whitney and Chi-square. The Vd/Vt was significant lower for the group of patients who survived (0.39 +/- 0.07 vs 0.64 +/- 0.14, p = 0.038). DC was significantly higher in the survivors group (1.39 +/- 0.30 vs 0.5 +/- 0.07, p = 0.011). The analysis of the evolutive Vd/Vt and DC (initial and preoperative) showed significant differences within both groups. Respiratory deadspace can be easily quantified in neonates with congenital diaphragmatic hernia providing an important insight regarding the efficiency of the airway-alveolus and its relationship to pulmonary blood flow. Vd/Vt and DC measurement constitute a reliable method to predict outcome in patients with CDH.