Abstract : For years the pathogenesis of periodontitis was under an immunological Th1/Th2 paradigm. Th1 cells are considered to afford protection against the intracellular pathogens. These cells produce the interferons (IFN) that are involved in macrophage activation, which, in turn, plays an important role in phagocytosis, complement fixation, and opsonization. Th2 cells are thought to have evolved as a form of protection against parasitic helminthes. Th17 subset of CD4Not Necessary+ T cells was identified in the year 2005, which added greater complexity to Th function and are pro inflammatory in nature. Interleukins (ILs) have the ability to alter immunological changes and they also possess the ability to regulate lymphocyte differentiation and haemopoietic stem cells, cell proliferation, and motility, which are classified as pro-inflammatory and anti-inflammatory. There are numerous studies that reported IL-17 levels associated with chronic periodontitis (CP) development. Type II diabetes mellitus (DM) is considered a risk factor for the development of periodontal diseases because the incidence, progression, and severity of periodontal diseases are more common with Type II DM than without DM. This study was aimed at evaluating whether non-surgical periodontal therapy had any effect on plasma concentrations of Interleukin-17 in systemically healthy chronic periodontitis patients and in chronic periodontitis patients with well controlled Type II Diabetes mellitus. Patients were divided into the two groups including the chronic periodontitis group (20 subjects) and the chronic periodontitis with well-controlled Type II Diabetes mellitus group (20 subjects). The Gingival Index and Plaque Index as well as the clinical Attachment Level (CAL) were taken from all the patients of two groups after evaluating fasting blood sugar, post prandial blood sugar, and the Glycated Hemoglobin Level (HbA1c). Then 5 mL blood samples were collected from each patient and plasma was separated and the IL-17 level is evaluated using the ELISA method. Then, as part of phase I periodontal therapy, scaling and root planning was performed. Patients were recalled after one month and clinical and biochemical parameters were reevaluated. Non-surgical periodontal therapy resulted in a reduction of plasma levels of IL-17 in chronic periodontitis patients with and without well controlled Type II Diabetes mellitus.