OBJECTIVE The aim of this study was to compare high-resolution manometry (HRM) and upper gastrointestinal (GI) endoscopy as diagnostic utilities in detecting a sliding hiatus hernia in patients with gastro-oesophageal reflux disease (GORD) symptoms. METHODS For both diagnostic modalities, the data obtained from 31 patients (20 females; mean age 48.2) who qualified for Nissen fundoplication were analysed using oesophageal pressure topography in line with the Chicago Classification. Confirmation of hiatus hernia during the surgery was considered the gold standard. HRM protocol involved 10 consecutive boluses of 10 mL of water. RESULTS Sliding hiatus hernia was confirmed intraoperatively in 29 out of 31 patients. In 14 patients, hiatus hernia was detected in HRM, while 19 patients were found to have hiatus hernia by upper GI endoscopy before surgery. No false positive results were obtained in HRM, while 15 false negative results were shown. In upper GI endoscopy, false positive data were observed in 1 patient, while false negative results were found in 10 patients. Thus, the sensitivity of HRM in detecting hiatus hernia was 48% (95%CIs: 29-67%), and sensitivity of upper GI endoscopy was 66% (95%CIs: 46-82%). It was not possible to assess the specificity of HRM or upper GI endoscopy because only 2 of 31 patients had no hiatus hernia during fundoplication (gold standard). False negative results (sensitivity) were not significantly different between compared diagnostic modalities HRM and upper GI endoscopy (52% vs. 34%, respectively, p = 0.29). CONCLUSIONS Due to poor sensitivity, both modalities, i.e., HRM and upper GI endoscopy, are not reliable tools to diagnose sliding hiatus hernia in patients with GORD symptoms.