Since esophageal length varies linearly with height, intraluminal pH monitoring can be performed at a position within the esophagus that is determined by an equation. Alternatively, pH probes can be positioned under fluoroscopic guidance, though no radiographic landmarks indicate the position that is 87% of esophageal length (where the monitoring is usually accomplished). Our aims were to determine whether a relationship might exist between crown-rump length and esophageal length, for use in patients in whom height is difficult or inappropriate to measure, and to determine whether the mid-right atrium can be used as a radiographic landmark in fluoroscopic pH probe placement. Height, crown-rump length, and distance from the suprasternal notch to the left anterior superior iliac spine were measured in 65 consecutive children undergoing 24-h pH monitoring. As the pH probe was inserted under fluoroscopy, distances from the nose to diaphragm and mid-right atrium were determined. Equations were derived by simple linear regression to describe the relationships between each of the body measurements and esophageal length. There is excellent correlation between crown-rump length and the distances from the nose to diaphragm and to mid-right atrium. The mid-right atrium corresponds to 87% of the nose to diaphragm distance in many patients.