Hiatal hernia (HH) is common in obese patients undergoing bariatric surgery. Preoperative traditional techniques such as upper gastrointestinal endoscopy (UGIE) or barium swallow/esophagram do not always correlate with intraoperative findings. High-resolution manometry (HRM) has shown a higher sensitivity and specificity than traditional techniques in non-obese patients in the HH diagnosis, whereas there is a lack of data in the morbidly obese population. We aimed to prospectively assess the diagnostic accuracy of HRM in HH detection, in comparison with barium swallow and UGIE, assuming intraoperative diagnosis as a standard of reference. Forty-one consecutive morbidly obese patients prospectively recruited from a tertiary-care referral hospital devoted to bariatric and metabolic surgery underwent a preoperative evaluation including standardized GERD questionnaires, barium swallow, UGIE, and HRM. The surgical procedures were performed by a single surgeon who was blinded to the results of other investigations. HH was intraoperatively diagnosed in 11/41 patients (26.8%). In 10/11 patients, the preoperative HRM showed an esophagogastric junction suggestive of HH. When compared to intraoperative evaluation, the sensitivity of the HRM was 90.9% and the specificity 63.3%, with a positive predictive value of 47.6% and a negative predictive value of 95.0%. HRM showed a higher sensitivity and specificity compared to barium swallow and UGIE. HRM has a high accuracy of HH detection in morbidly obese patients assuming an intraoperative diagnosis as reference standard. It could therefore be a very useful tool in the preoperative work-up of obese patients undergoing bariatric surgery.