| K20 | Esophagitis |
| K20.0 | Eosinophilic esophagitis |
| K20.8 | Other esophagitis |
| K20.9 | Esophagitis, unspecified |
| K21 | Gastro-esophageal reflux disease |
| K21.0 | Gastro-esophageal reflux disease with esophagitis |
| K21.9 | Gastro-esophageal reflux disease without esophagitis |
| K22 | Other diseases of esophagus |
| K22.0 | Achalasia of cardia |
| K22.1 | Ulcer of esophagus |
| K22.10 | Ulcer of esophagus without bleeding |
| K22.11 | Ulcer of esophagus with bleeding |
| K22.2 | Esophageal obstruction |
| K22.3 | Perforation of esophagus |
| K22.4 | Dyskinesia of esophagus |
| K22.5 | Diverticulum of esophagus, acquired |
| K22.6 | Gastro-esophageal laceration-hemorrhage syndrome |
| K22.7 | Barrett's esophagus |
| K22.70 | Barrett's esophagus without dysplasia |
| K22.71 | Barrett's esophagus with dysplasia |
| K22.710 | Barrett's esophagus with low grade dysplasia |
| K22.711 | Barrett's esophagus with high grade dysplasia |
| K22.719 | Barrett's esophagus with dysplasia, unspecified |
| K22.8 | Other specified diseases of esophagus |
| K22.9 | Disease of esophagus, unspecified |
| K23 | Disorders of esophagus in diseases classified elsewhere |
| K25 | Gastric ulcer |
| K25.0 | Acute gastric ulcer with hemorrhage |
| K25.1 | Acute gastric ulcer with perforation |
| K25.2 | Acute gastric ulcer with both hemorrhage and perforation |
| K25.3 | Acute gastric ulcer without hemorrhage or perforation |
| K25.4 | Chronic or unspecified gastric ulcer with hemorrhage |
| K25.5 | Chronic or unspecified gastric ulcer with perforation |
| K25.6 | Chronic or unspecified gastric ulcer with both hemorrhage and perforation |
| K25.7 | Chronic gastric ulcer without hemorrhage or perforation |
| K25.9 | Gastric ulcer, unspecified as acute or chronic, without hemorrhage or perforation |
| K26 | Duodenal ulcer |
| K26.0 | Acute duodenal ulcer with hemorrhage |
| K26.1 | Acute duodenal ulcer with perforation |
| K26.2 | Acute duodenal ulcer with both hemorrhage and perforation |
| K26.3 | Acute duodenal ulcer without hemorrhage or perforation |
| K26.4 | Chronic or unspecified duodenal ulcer with hemorrhage |
| K26.5 | Chronic or unspecified duodenal ulcer with perforation |
| K26.6 | Chronic or unspecified duodenal ulcer with both hemorrhage and perforation |
| K26.7 | Chronic duodenal ulcer without hemorrhage or perforation |
| K26.9 | Duodenal ulcer, unspecified as acute or chronic, without hemorrhage or perforation |
| K27 | Peptic ulcer, site unspecified |
| K27.0 | Acute peptic ulcer, site unspecified, with hemorrhage |
| K27.1 | Acute peptic ulcer, site unspecified, with perforation |
| K27.2 | Acute peptic ulcer, site unspecified, with both hemorrhage and perforation |
| K27.3 | Acute peptic ulcer, site unspecified, without hemorrhage or perforation |
| K27.4 | Chronic or unspecified peptic ulcer, site unspecified, with hemorrhage |
| K27.5 | Chronic or unspecified peptic ulcer, site unspecified, with perforation |
| K27.6 | Chronic or unspecified peptic ulcer, site unspecified, with both hemorrhage and perforation |
| K27.7 | Chronic peptic ulcer, site unspecified, without hemorrhage or perforation |
| K27.9 | Peptic ulcer, site unspecified, unspecified as acute or chronic, without hemorrhage or perforation |
| K28 | Gastrojejunal ulcer |
| K28.0 | Acute gastrojejunal ulcer with hemorrhage |
| K28.1 | Acute gastrojejunal ulcer with perforation |
| K28.2 | Acute gastrojejunal ulcer with both hemorrhage and perforation |
| K28.3 | Acute gastrojejunal ulcer without hemorrhage or perforation |
| K28.4 | Chronic or unspecified gastrojejunal ulcer with hemorrhage |
| K28.5 | Chronic or unspecified gastrojejunal ulcer with perforation |
| K28.6 | Chronic or unspecified gastrojejunal ulcer with both hemorrhage and perforation |
| K28.7 | Chronic gastrojejunal ulcer without hemorrhage or perforation |
| K28.9 | Gastrojejunal ulcer, unspecified as acute or chronic, without hemorrhage or perforation |
| K29 | Gastritis and duodenitis |
| K29.0 | Acute gastritis |
| K29.00 | Acute gastritis without bleeding |
| K29.01 | Acute gastritis with bleeding |
| K29.2 | Alcoholic gastritis |
| K29.20 | Alcoholic gastritis without bleeding |
| K29.21 | Alcoholic gastritis with bleeding |
| K29.3 | Chronic superficial gastritis |
| K29.30 | Chronic superficial gastritis without bleeding |
| K29.31 | Chronic superficial gastritis with bleeding |
| K29.4 | Chronic atrophic gastritis |
| K29.40 | Chronic atrophic gastritis without bleeding |
| K29.41 | Chronic atrophic gastritis with bleeding |
| K29.5 | Unspecified chronic gastritis |
| K29.50 | Unspecified chronic gastritis without bleeding |
| K29.51 | Unspecified chronic gastritis with bleeding |
| K29.6 | Other gastritis |
| K29.60 | Other gastritis without bleeding |
| K29.61 | Other gastritis with bleeding |
| K29.7 | Gastritis, unspecified |
| K29.70 | Gastritis, unspecified, without bleeding |
| K29.71 | Gastritis, unspecified, with bleeding |
| K29.8 | Duodenitis |
| K29.80 | Duodenitis without bleeding |
| K29.81 | Duodenitis with bleeding |
| K29.9 | Gastroduodenitis, unspecified |
| K29.90 | Gastroduodenitis, unspecified, without bleeding |
| K29.91 | Gastroduodenitis, unspecified, with bleeding |
| K30 | Functional dyspepsia |
| K31 | Other diseases of stomach and duodenum |
| K31.0 | Acute dilatation of stomach |
| K31.1 | Adult hypertrophic pyloric stenosis |
| K31.2 | Hourglass stricture and stenosis of stomach |
| K31.3 | Pylorospasm, not elsewhere classified |
| K31.4 | Gastric diverticulum |
| K31.5 | Obstruction of duodenum |
| K31.6 | Fistula of stomach and duodenum |
| K31.7 | Polyp of stomach and duodenum |
| K31.8 | Other specified diseases of stomach and duodenum |
| K31.81 | Angiodysplasia of stomach and duodenum |
| K31.811 | Angiodysplasia of stomach and duodenum with bleeding |
| K31.819 | Angiodysplasia of stomach and duodenum without bleeding |
| K31.82 | Dieulafoy lesion (hemorrhagic) of stomach and duodenum |
| K31.83 | Achlorhydria |
| K31.84 | Gastroparesis |
| K31.89 | Other diseases of stomach and duodenum |
| K31.9 | Disease of stomach and duodenum, unspecified |