The entire gastroesophageal junction of 36 patients who had been operated for squamous cell carcinoma of the upper or middle esophagus was examined. Hematoxylin and eosin-stained slides were evaluated by two pathologists for the following histologic details: minimal and maximal length of cardiac mucosa (CM) and oxyntocardiac mucosa (OCM, mixture of cardiac and fundic glands), degree of inflammation in CM and OCM, and presence of intestinal metaplasia or pancreatic metaplasia. Sections of gastric corpus mucosa were evaluated for the presence of gastritis and infection; sections of esophageal squamous epithelium were evaluated for the presence of reflux esophagitis. CM was present in the entire circumference of the gastroesophageal junction in 20 cases, in parts of the circumference in 15 cases, and entirely absent in one case. The maximal length per case ranged between 1 and 15 mm (median 5 mm). OCM was circumferentially present in 22 cases and partially present in 14 cases. The maximal length ranged between 2 and 24 mm (median 7 mm). Locations of CM/OCM over submucosal esophageal glands or squamous epithelium-lined ducts, both indicating a location in the esophagus, were found in eight cases (22%) and in four cases (11%), respectively. In 18 cases (50%) intestinal metaplasia was present in CM/OCM; pancreatic metaplasia was found in 22 cases (61%). A statistically not significant trend for increase of minimal length of CM, OCM, and the sum of both was found in the presence of gastroesophageal reflux disease. Neither the presence of intestinal metaplasia nor of pancreatic metaplasia in CM/OCM was correlated with gastroesophageal reflux disease. In conclusion, the high variability in length, the frequent occurrence of intestinal metaplasia and pancreatic metaplasia, and the frequent extension into the esophagus suggest that CM/OCM is a dynamic structure that probably mirrors the influence of underlying gastroesophageal diseases. Because of the short length and incomplete circumferential extension of CM/OCM, future endoscopic-bioptic investigations will probably have to be based on more extensive sampling of the gastroesophageal junction.