One hundred and sixty patients with head and neck carcinomas were followed from one to 15 years to assess the associations between tobacco usage and the development of multiple head and neck cancers. Seventy-three percent had tobacco habits, with nine of ten users smoking cigarettes. In almost one in five patients (18.1%), second primary oral/oropharyngeal cancers developed in a mean time of five years. Those who did not change their original tobacco habits incurred the greatest risk, as a second primary cancer developed in 30%. Reducing or discontinuing smoking appeared to have a beneficial effect. There was also an increased risk for multiple cancers in males, probably because of their larger amount of daily smoking.