A higher risk for the development of oral cancer was associated with heavy smoking and heavy drinking, but alcohol drinking and tobacco smoking are also correlated with other oral cavity disease. Tobacco is the most important factor of leukoplakia, but other diseases like ANUG, periodontitis, median rhomboid glossitis, chronic hyperplastic candidiasis and others are also correlated to cigarette smoking. It was observed that smokers have more plaque than non-smokers, even if no difference in the bacteria composition was found between smokers and non-smokers samples, and the vascular reaction associated with plaque induced gingivitis is suppressed in smokers. Periodontitis are generally considered to be a consequence of an unfavourable host-parasite interaction, but personal factors that diminish the efficiency of the host defence, like tobacco smoking and alcohol drinking, can play an important role in the development of periodontal diseases. Cigarette smoking may be considered a major risk factor for periodontitis and it can also increase its severity; therefore, alveolar bone loss increases with tobacco smoking. Recent investigations show that smokers respond less favourably than no smokers to the different modalities of periodontal therapy, as surgical and non surgical, or guided tissue regeneration. Moving from these observations the authors critically analyze the literature concerning these important risk factors which appear to be strongly correlated with periodontal diseases.