Abstract The clinical diagnosis of sliding hiatal hernia is usually based on x-ray examination. The accuracy of the radiologic interpretation is questionable since the reported incidence varies from 1 to 67 per cent. Manometric and radiologic techniques were utilized in the study of 21 cases with previous x-ray diagnosis of hiatal hernia in an effort to determine the validity of such diagnoses. In 3 cases, the lower margin of the vestibule, the most distal portion of the esophagus, was displaced above the hiatus; thus confirming the diagnosis of hiatal hernia. In 5 cases the vestibule could not be accurately identified and these cases remained unclassified. In 13 cases the lower margin of the vestibule was either 1 to 2 cm. below or at the hiatus. Since the esophagus was in its normal position, no protrusion of stomach into the thoracic cavity, i.e., no sliding hiatal hernia, was present. Furthermore, it was observed that barium collected in the lower esophagus in a manner mimicking hiatal hernia. The simultaneous motility records showed that the parts of the esophagus involved in the pseudohernia appearance were the vestibule and the distal part of peristaltic esophagus. It was suggested that when emptying of the lower esophagus is delayed, an irregular pouch mimicking hernia was formed and that this could be because of a relative imbalance between the degree of vestibular relaxation as compared with the strength of peristaltic contraction.