Squamous cell carcinoma is the most common malignant tumor of the esophagus and it is one of the most common fatal cancers worldwide. There is great geographic variation in occurrence of these tumors. Especially high-risk areas have been identified in Northern Iran, Central Asian Republics, Northern China and South Africa. In some of these areas annual mortality rates reach 133/100,000 and over 20% of the population dies of esophageal cancer. The mortality in the US is considerably lower (3 to 8 per 100,000). In common with squamous dysplasias elsewhere eg the cervix, squamous dysplasia of the esophagus also appears to be a precancerous lesion. We have found that squamous dysplasia and early cancer are characterized by a number of distinctive endoscopic changes, namely, mucosal friability, erosions, plaques and nodules. Another finding of interest is the failure on our part to confirm the frequency of esophagitis in high risk areas. Barrett's esophagus is an epithelial metaplasia which replaces esophageal squamous epithelium for variable lengths from the lower esophageal sphincter region cephalad. It is a complication that occurs in approximately 12% of patients with prolonged gastroesophageal reflux. The importance of this disorder is that it is associated with an increased risk of adenocarcinoma of the esophagus. In assessing biopsies from patients with Barrett's esophagus, the main role of the pathologist is to be on the alert for histologic features of dysplasia and adenocarcinoma. Since dysplasia in Barrett's is endoscopically invisible, multiple biopsies are necessary if surveillance is to be successful in detecting dysplastic lesions and early carcinoma.(ABSTRACT TRUNCATED AT 250 WORDS)