Book excerpt: A working group of sixteen experts from seven countries re-evaluated the evidence of the carcinogenicity of betel-quid and areca-nut chewing and some areca-nut related nitrosamines. Betel-quid and areca-nut chewing are widely practised in many parts of Asia and in Asian-migrant communities elsewhere in the world. There are hundreds of millions of users worldwide. They evaluated betel quid with tobacco as carcinogenic to humans (Group 1) on the basis of sufficient evidence of an increased risk of cancer of the oral cavity, pharynx and oesophagus. The working group reviewed epidemiological studies of human cancer, mainly studies from India, Pakistan and Taiwan (China). Studies on betel quid with tobacco and areca nut with tobacco in experimental animals now also provide sufficient evidence of carcinogenicity. The working group also evaluated betel quid without tobacco as carcinogenic to humans (Group 1), on the basis of sufficient evidence of an increased risk of oral cancer. Studies on betel quid without tobacco and areca nut without tobacco in experimental animals now also provide sufficient evidence of carcinogenicity. Areca nut, a common ingredient of betel quid and many different chewing preparations, including those available commercially, has been observed to cause oral submucous fibrosis