The compliance of the respiratory system was determined at an average of 2.89 h (range 45 min – 8 h) after birth in 82 newborns who were retrospectively divided into group 1: healthy newborns (mean gestational age 37.1 weeks, range 30–41 weeks); group 2: newborns with respiratory distress (RD) needing no ventilatory support (mean gestational age 37.3 weeks, range 35–40 weeks); group 3: newborns with RD needing ventilatory support and surviving (mean gestational age 34.3 weeks, range 30 – 39 weeks), and group 4: newborns with RD who needed ventilatory support and died (mean gestational age 30’.8 weeks, range 28 – 37 weeks). Respiratory compliance was measured by the airway occlusion technique in spontaneously breathing babies and by injecting a known volume of gas into the closed airway system and measuring airway pressure in intubated babies. The difference in postnatal compliance was statistically significant (p < 0.01) in those four groups and was correlated with the severity of the disease in groups 2 and 3. In infants with RD, compliance was highly predictive for the need for ventilatory support (93% correct and 7% erroneous) and in infants with ventilatory support, for the mortality (83% correct and 17% erroneous). We conclude that postnatal compliance measurements are very useful to predict the course and outcome as well as to classify the sev