Chronic periodontopathies and diabetes mellitus are two clinical entities, which reciprocally condition one another. The periodontal disease is considered a major complication, which induces an unfavorable evolution of diabetes mellitus. Diabetes mellitus is an endocrine disease which favors the occurrence of periodontopathy through gum's microvascular disorders, the selection and development of an aggressive bacterial plaque and through an exaggerate inflammatory response to the microflora within the oral cavity. Both diabetes mellitus and periodontal disease have an increasing incidence in the whole world. Development of periodontopathy is related to the aggression of bacterial flora in dental plaque, flora that is influenced on its turn by the evolution of diabetes mellitus. In our study, we have evaluated the inflammatory reaction in periodontium in patients with slowly and progressive periodontitis in patients with diabetes mellitus who had diabetes longer than five years. It has been found that all patients presented a chronic inflammatory infiltrate, abundant, with round mononuclear cells of lymphocyte, plasma cells and macrophage type, with non-homogenous arrangement, more intensely where the covering epithelium presented erosions or necrotic areas. Out of the immunity system cells, the most numerous where of T-lymphocytes type.