Development and validation of an index for scoring baseline respiratory disease in the very low birth weight neonate. Severity Index Development and Validation Panels and Newborn Lung Project. An accurate description of the population at risk for neonatal chronic lung disease is clearly of prime importance for comparative studies and the planning of interventions. Attempts to explain variations in chronic lung disease rates in such studies have been compromised by lack of a way of estimating the severity of the initial pulmonary disease as a risk factor. Therefore, a severity index was developed for use in very low birth weight (less than 1501 g) neonates. Special emphasis was placed on applicability of the index in the multicenter observational setting. Development followed a clinician panel approach, with the resulting index designed to capture clinical judgment of severity. The index was validated prospectively on neonates in a neonatal intensive care unit, and retrospectively using charts from nine hospitals nationwide. Correlations of the index with clinical judgment in the two samples were .95 and .93, respectively. In an additional validation the index combined with birth weight correctly predicted oxygen dependence status at 30 days in 36 of 42 neonates consecutively admitted to five neonatal intensive care units (P = .002). Birth weight and the severity index contributed about equally to the prediction, and therefore they seem to represent partly independent components of baseline propensity for prolonged oxygen dependence. 