BACKGROUND The diagnosis of a sliding hiatal hernia is classically made with endoscopy or barium esophagogram. Spatial separation of the lower esophageal sphincter (LES) and diaphragm, the hallmark of hiatal hernia, can also be observed on high-resolution manometry (HRM), but the diagnostic accuracy of this finding has not yet been investigated. To determine the diagnostic value of HRM in the detection of hiatal hernia. METHODS HRM recordings, endoscopy reports, and barium esophagograms of 90 patients were analyzed for the presence and size of a hiatal hernia. The diagnostic value of a hernia specific HRM pressure pattern was calculated, and the agreement of HRM with endoscopy and barium esophagogram for the assessment of hernia size. RESULTS HRM was found to be highly sensitive and specific for hiatal hernia detection, with a sensitivity of 92% and specificity of 95%, exceeding the sensitivity of endoscopy or radiography alone (both 73%). Patients with a hiatal hernia on HRM were manometrically characterized by an esophagogastric junction (EGJ) with partial or complete separation of the LES and crural diaphragm (CD), the latter being associated with significantly lower EGJ pressure. A cutoff value of spatial LES-CD separation on HRM of 1.85 cm yielded the optimal performance in identifying hiatal hernia. Agreement between HRM, endoscopy, and radiography for size of hiatal hernias was good (ICC [95% CI] 0.74 [0.65-0.82]). CONCLUSIONS With HRM, the presence or absence and size of a hiatal hernia can be assessed with greater sensitivity than with endoscopy or radiography alone.