We have noted that sonographically positive cases of hypertrophic pyloric stenosis (HPS) demonstrate a distortion of normal anatomy in which the elongated pylorus displaces the duodenum and lies adjacent to and below the gallbladder. Ten consecutive cases of HPS diagnosed by ultrasound were reviewed. In each case the pylorus was imaged subjacent to the gallbladder. Sonograms from 100 infants from a different institution were then reviewed. There were 13 cases with the pylorus subjacent to the gallbladder, 12 of these met criteria for HPS. Recognition of this anatomic relationship may aid in the diagnosis of HPS.