The oral cavity and pharynx combined is the sixth commonest site of cancer in both sexes. In many countries the mortality rate is increasing among younger men born since approximately 1910-1920. A causal role in the aetiology of mouth cancer has been established for tobacco use, both smoking and chewing, separately and in conjunction with betel-quid chewing; with alcohol consumption and, less certainly, with other factors such as poor oral hygiene, nutritional factors and certain occupational exposures. In Western countries, there is convincing evidence that a large attributable risk can be ascribed to the joint habits of cigarette smoking and alcohol consumption. In Asian societies, a high attributable risk can be ascribed to cigarette smoking and betel chewing. Mouth cancer is at the same time an important form of cancer, and one for which practical prospects for prevention already exist. Against this background of a continually increasing trend among younger persons, it seems essential to engage upon programmes of prevention, including increasing awareness for early detection, against mouth cancer at the present time.