In the upper aerodigestive tract, carcinogenesis in squamous cell muco
sa is characterized by a tendency to field cancerization leading to mu
lticentricity of lesions and synchronous or metachronous multiple tumo
ral lesions, namely multifocality. During pretherapy bronchoesophagosc
opy carried out on ENT-cancer patients, the rate of synchronous second
primary cancer is 24%. In 85% of the cases, these second primaries ar
e detected at an early stage (in situ, microinvasive or submucosal car
cinoma) and do not give rise to symptoms. Early diagnosis of cancer of
the upper aerodigestive tract is possible provided that high risk pat
ients are recognized and screening endoscopy of the whole mucosa is pe
rformed in every high risk patient. On the other hand, squamous cell c
arcinoma and adenocarcinoma may occur with increased frequency in pati
ents with esophageal lesions such as achalasia, caustic stenosis and B
arrett's esophagus. The premalignant potential of these three entities
is discussed.