In the upper aerodigestive tract, carcinogenesis in squamous cell mucosa is characterized by a tendency to field carcinogenesis leading to multicentricity of lesions and synchronous or metachronous multiple tumoral lesions, namely multifocality. During pretherapy broncho-esophagoscopy carried out on ENT-cancer patients, the rate of synchronous second primary cancer is 24%. In 85% of the cases, these second primaries are detected at an early stage (in situ, microinvasive or submucosal carcinoma) and do not give rise to symptoms. Early diagnosis of cancer of the upper aerodigestive tract is possible provided that high risk patients are recognized and screening endoscopy of the whole mucosa is performed in every high risk patient. On the other hand, squamous cell carcinoma and adenocarcinoma may occur with increased frequency in patients with esophageal lesions such as achalasia, caustic stenosis and Barrett's esophagus. The premalignant potential of these three entities is discussed.