OBJECTIVE: The aim of the study was to investigate the impact of the size of the esophageal hiatus on lower esophageal sphincter pressure (LESP) and acid reflux. METHODS: Patients with gastroesophageal reflux disease who underwent Nissen fundoplication in 2006-2008 were included. All underwent esophageal manometry and 22 had 24-h pH monitoring. The area of the esophageal hiatus was calculated from a photograph shot during surgery. A hiatal index was calculated via division of hiatal area with body mass index (BMI). Correlation and logistic regression analysis were performed. RESULTS: Twenty-eight patients (average age 44, 14 males) were enrolled. The mean BMI, LESP, DeMeester score, hiatal area, and hiatal index were 27 +/- 3.9 kg/m(2), 11.7 +/- 6.6 mmHg, 43 +/- 34, 3.83 +/- 1.24 cm(2), and 0.143 +/- 0.048, respectively. There was a significant negative correlation between hiatal area, hiatal index and LESP (-0.513, p = 0.005, r = -0.439, p = 0.019 respectively). Additionally there was a negative correlation between hiatal area and total LES length (r = -0.508, p = 0.013) and a significant positive correlation between hiatal area, hiatal index, and DeMeester scores (0.452, p = 0.035, 0.537, p = 0.01, respectively). Height and hiatal area were significant factors in multiple linear regression. CONCLUSIONS: The size of the esophageal hiatus significantly affects LESP and acid reflux, and hiatal index is a new value, which appears to reflect the amount of acid reflux. Total LES length is also shortened in patients with a large hiatus.