A hiatal hernia (HH) is a frequent finding in patients with gastroesophageal reflux disease (GERD). We examined a consecutive series of patients with GERD diagnosed by a 24-hour pH monitoring. Based on the presence and size of HH on barium swallow, patients were divided into the following groups: no HH, HH <3 cm, HH 3-5 cm and HH >5 cm. A total of 175 patients were included: 43 with no HH, 86 with HH <3 cm, 34 with HH 3-5 cm, and 12 with HH >5 cm. Patients with larger HH had more frequent episodes of coughing and wheezing associated with episodes of reflux. High-resolution manometry showed that the increasing size of the HH was associated with decreasing pressure of the lower esophageal sphincter and weaker peristalsis. Ambulatory pH monitoring revealed that patients with larger HH had more acid reflux, in both the distal and proximal esophagus. Endoscopy showed that patients with larger HH had more severe esophagitis. Fifty per cent of patients with HH >5.0 cm had Barrett's esophagus. These findings should guide gastroenterologists and surgeons in choosing the appropriate therapy in patients with GERD and large HH.