A prospective study of the incidence of hiatus hernia and/or reflux oesophagitis was carried out in 670 patients referred for routine upper alimentary endoscopy. Hiatus hernia was found in 16.6% and reflux oesophagitis in 15.1% of the patients. Forty-two per cent of the patients with hernia did not have oesophagitis, whereas 63% of the patients with reflux oesophagitis had hernia. In patients without reflux oesophagitis the incidence of hiatus hernia was 8%. Reflux oesophagitis was significantly (p less than 0.001) related to hiatus hernia. The severity of the oesophagitis was significantly (p less than 0.05) related to the presence and the size of hernia, and severe oesophagitis without hernia was significantly (p less than 0.01) related to chronic alcoholism. The results suggest that a sliding hiatus hernia may play a role in the development of reflux oesophagitis.