Smoking is a recognized risk factor for human health. It is related to many conditions such as respiratory problems, cardiovascular DISEASES and cancer. Cigarette smoking represents a major preventable cause of human disease. Cigarette smoking is a well-known risk factor for several oral DISEASES, including a widely studied and established association with PERIODONTAL DISEASES. Although the direct cause for periodontitis is oral bacterial infection, its progression and severity depend on a number of genetic and environmental factors. Cigarette smoking is arguably the strongest behavioral risk factor for the incidence and progression of periodontitis Tobacco and some of its components such as nicotine have been found to have adverse effects on cells of the periodontium, including gingival fibroblasts and cells of the immune system. An in vitro study done by Tanur et al. showed that the nature of cell attachment to root surfaces is altered by nicotine Cigarette smoking is likely to affect the composition of the oral microflora due to a decrease in oxygen tension in PERIODONTAL pockets and may lead to a selection of anaerobic bacteria Tobacco smoking affects the humoral mediated and the cell mediated immunity of the host and this may increase susceptibility to PERIODONTAL disease. Smoking has profound consequences on the immune and inflammatory systems. Smoking has adverse effects on fibroblast function, chemotaxis, and phagocytosis by neutrophils and immunoglobulin production. There is evidence for an impact of smoking on bone metabolism such as an increased secretion of the bone resorbing factors PGE2 and IL-1β or a decreased intestinal uptake of calcium Smoking has a strong negative impact on regenerative therapy, including osseous grafting, guided tissue regeneration, or a combination of these treatments the oral cancer risk is higher in smokers. The risk is related to the amount and duration of smoking. Smoking can cause DNA instability. This is in consistent with increasing counts of mucosal micronucleus Decrease in capillary diameter and density of blood vessels in the gingival tissues of smokers explains the reduction of redness and bleeding.