OBJECTIVE To evaluate the relationship between oesophageal hiatus surface area (OHSA) and gastro-oesophageal reflux disease (GERD). METHODS Patients who underwent 24-h pH monitoring, oesophageal high-resolution manometry, and upper abdominal contrast-enhanced multidetector computed tomography (MDCT) during 2014-2021 were enrolled. Patients with a hiatus hernia (HH) on MDCT or who had a history of gastro-oesophageal surgery were excluded. Multiplanar reconstruction (MPR) of the MDCT image was used for the measurement of OHSA. Correlations of OHSA with acid exposure time (AET) and lower oesophageal sphincter (LOS) pressure of all patients were analysed. RESULTS Seventy-eight patients were included in the study. OHSA was much less in the AET <4% group than in the AET >6% group (1.61 ± 0.42 versus 2.09 ± 0.55 cm2, p<0.001). Correlation analysis reveals that OHSA correlated positively with AET (correlation coefficient = 0.47, p<0.001). Receiver operating characteristic (ROC) curve analysis reveals that OHSA can significantly distinguish patients in different groups divided by AET (area under the ROC curve [AUC] = 0.76, 95% confidence interval [CI]: 0.63-0.90). OHSA was not related to LOS pressure (correlation coefficient = -0.268, p=0.051). There was no difference in OHSA between the low LOS pressure group and the normal LOS pressure group (1.84 ± 0.61 versus 1.74 ± 0.50 cm2, p=0.52). CONCLUSIONS OHSA significantly correlated with AET but has no relationship with LOS pressure. It may be an independent risk factor of GERD.