| K12 | Stomatitis and related lesions |
| K120 | Recurrent oral aphthae |
| K121 | Other forms of stomatitis |
| K122 | Cellulitis and abscess of mouth |
| K123 | Oral mucositis (ulcerative) |
| K1230 | Oral mucositis (ulcerative), unspecified |
| K1231 | Oral mucositis (ulcerative) due to antineoplastic therapy |
| K1232 | Oral mucositis (ulcerative) due to other drugs |
| K1233 | Oral mucositis (ulcerative) due to radiation |
| K1239 | Other oral mucositis (ulcerative) |
| K13 | Other diseases of lip and oral mucosa |
| K130 | Diseases of lips |
| K131 | Cheek and lip biting |
| K132 | Leukoplakia and other disturbances of oral epithelium, including tongue |
| K1321 | Leukoplakia of oral mucosa, including tongue |
| K1322 | Minimal keratinized residual ridge mucosa |
| K1323 | Excessive keratinized residual ridge mucosa |
| K1324 | Leukokeratosis nicotina palati |
| K1329 | Other disturbances of oral epithelium, including tongue |
| K133 | Hairy leukoplakia |
| K134 | Granuloma and granuloma-like lesions of oral mucosa |
| K135 | Oral submucous fibrosis |
| K136 | Irritative hyperplasia of oral mucosa |
| K137 | Other and unspecified lesions of oral mucosa |
| K1370 | Unspecified lesions of oral mucosa |
| K1379 | Other lesions of oral mucosa |
| K14 | Diseases of tongue |
| K140 | Glossitis |
| K141 | Geographic tongue |
| K142 | Median rhomboid glossitis |
| K143 | Hypertrophy of tongue papillae |
| K144 | Atrophy of tongue papillae |
| K145 | Plicated tongue |
| K146 | Glossodynia |
| K148 | Other diseases of tongue |
| K149 | Disease of tongue, unspecified |
| K20 | Esophagitis |
| K200 | Eosinophilic esophagitis |
| K208 | Other esophagitis |
| K2080 | Other esophagitis without bleeding |
| K2081 | Other esophagitis with bleeding |
| K209 | Esophagitis, unspecified |
| K2090 | Esophagitis, unspecified without bleeding |
| K2091 | Esophagitis, unspecified with bleeding |
| K21 | Gastro-esophageal reflux disease |
| K210 | Gastro-esophageal reflux disease with esophagitis |
| K2100 | Gastro-esophageal reflux dis with esophagitis, without bleed Gastro-esophageal reflux disease with esophagitis, without bleeding |
| K2101 | Gastro-esophageal reflux disease with esophagitis, with bleeding |
| K219 | Gastro-esophageal reflux disease without esophagitis |
| K22 | Other diseases of esophagus |