There is little evidence of a strong effect of familial and genetic predisposition to oral cancer. Lip cancer is among the sites that show the strongest cancer clustering within families in the genealogical records of the Utah database, the others being leukemia, lobular breast cancer, early melanoma and adenocarcinomas of the lung in females. For cancer of the tongue, there was some evidence of increased isonomy within but not between regions. Although this could result from inherited susceptibility clustering in different regions, a more likely explanation is that environmental risk factors such as tobacco and alcohol will be common to families. For cancer of the salivary glands there was increased isonomy both within and between regions, again suggesting but not proving that genetic factors are involved; this however is consistent with reports of familial occurrence of malignant salivary tumours.