Objective . To compare whether early measurement of blood gases and/or dynamic compliance of the respiratory system (CRS_dyn) predicts outcome in high-risk infants with unilateral congenital diaphragmatic hernia (CDH). Patients and methods. A retrospective study was performed at Tygerberg Children’s Hospital between January 1992 and August 2001. High-risk infants with unilateral CDH, who presented with respiratory distress within 6 hours of birth, were included. Patients with other lethal congenital abnormalities were excluded. The first arterial blood gas value after endotracheal intubation was documented and the arterial-alveolar oxygen tension (a:A) ratio was calculated. CRS_dyn was measured within 24 hours of birth. The ability of these measurements to predict outcome (survival or death during the newborn period) was determined. Results . Seventeen of 40 infants with CDH were categorised as high risk and included in the study. Eight of them (47%) survived the neonatal period. The best single predictors of outcome were, in order, partial pressure of oxygen in arterial blood (PaO₂), a:A ratio and dynamic compliance of the respiratory system standardised for body weight (CRS_dyn/kg). The specificity and sensitivity at a PaO₂ cut-off of 19.3 kPa were 7/8 (95% confidence interval (CI): 0.473 - 0.997) and 9/9 (95% CI: 0.634 - 1.000) respectively. Results for a:A ratio were cut-off 0.321, specificity 6/8 (95% CI: 0.349 - 0.968), and sensitivity 9/9 (95% CI: 0.634 - 1.000). Results for CRS_dyn/kg were cut-off 0.259, specificity 6/8 (95% CI: 0.349 - 0.968), and sensitivity 9/9 (95% CI: 0.634 - 1.000). A linear discriminant function based on the 3 best single predictors was found to be no more effective than the first PaO₂. Conclusions . Early oxygenation status predicts outcome better than the CRS_dyn/kg in infants with unilateral CDH. However, both measurements predict outcome with high accuracy.