Objectives: Strobel’s formula (Esophageal length = 5 + 0.252 × Height) is frequently used as a guide for determining the distance from the nares to the lower esophageal sphincter (LES) in term infants. The aim of this study was to examine this relationship in premature infants. Study design: The distance from nares to LES was manometrically determined in 156 premature infants (26-40 weeks’ postmenstrual age; body weights of 610-3050 g). The ability of body weight, height (body length), head circumference, and postmenstrual age to predict the manometrically determined LES position was evaluated with linear and non-linear regression analyses. Results: Body weight and body length were the most predictive of distance from nares to LES (r² = 0.848 and 0.802, respectively). These relationships were non-linear and, in the case of body length, deviated substantially from Strobel’s model. Conclusions: In premature neonates, a different formula is needed for prediction of the distance between nares and LES than that applied to term infants and children. (J Pediatr 1999;135:522-5)