It is believed that there is a co-relation between periodontal diseases and systemic diseases such as diabetes mellitus, pregnancy, smoking and local factors such as drugs.Certain systemic conditions clearly may affect the initiation and progression of gingivitis and Periodontitis. Systemic disorders affecting neutrophils, monocytes/ macrophages and lymphocytes function results in altered production activity of host inflammatory mediators. Hence this current text offers a contemporary guide to explain the mechanism and effects of such diseases on Periodontium.