In many cases, the oral health status indicates the general status of the body. 90% of the disorders of the body also manifest at the level of the oral cavity, which means that the dentist can draw the attention of a certain health problem. Diabetes mellitus is associated with a high prevalence of the lesions of the oral mucous, especially lichen planus, recurrent aphthous stomatitis or oral candidiasis. We present here a case of diabetes mellitus with hyperplasic lesion at the level of the inferior vestibule, extended to the right jugal mucosa. The lesion appeared pursuant to the application of removable prosthetics. The biopsy specimen was examined using normal and special staining (HE Hematoxiline - eosine, Van Gieson VG) and immunohistochemistry (IHC). In the HE stain, an epithelial hyperplasia was noticed as a result of the proliferation of the basal cells, associated with hyperkeratosis (parakeratosis or orthokeratosis). A moderated inflammatory limphoplasmocitary infiltrate, composed by lymphocytes and plasma cells, was present within the hyperplasic chorion. The immunohistochemical reactions revealed Ki-67 positive nuclei in the basal and suprabasal strata (indicating an increased proliferating activity); rare p53 positive nuclei in the basal stratum (indicating a suppressive action on the cell proliferation); CD3/CD8 positive cells in the inflammatory infiltrate (indicating an important number of T suppressor lymphocytes in the inflammatory infiltrate). In conclusion, diabetes mellitus is a disease which frequently determines major modifications at the level of the oral cavity. Interdisciplinary collaboration between the pathologist and the dentist is necessary for adequate diagnosis and successful treatment.