Recommendations for preventing adenocarcinoma: The standard definition of Barrett's epithelium should be the presence of intestinalized mucosa in the lower esophagus. Patients in this category should be considered for inclusion in a screening program for the detection of dysplasia or carcinoma. Those who are a poor operative risk should not be screened if the detection of an end-point such as high-grade dysplasia or intramucosal carcinoma will still not lead to resection. In some centers, however, alternative experimental methods of mucosal ablation may be available. The endpoint for screening is invasive or intramucosal carcinoma (or--in centers with a very low operative mortality--high-grade dysplasia). These should lead to consideration of surgery or, in specialized centers and as part of controlled studies, newer alternative modes of epithelial ablation. Intermediate markers, e.g., use of aneuploidy, gene markers, or their products, are at present experimental. Screening should be carried out annually or, possibly, biennially. This screening should utilize a standard protocol with an endoscope capable of obtaining large-particle biopsies. Four quadrant biopsies should be taken about every 2 cm, beginning 2 cm above the proximal limit of the gastric rugae, continuing until unequivocally in squamous mucosa, and following any tongues of glandular epithelium. Recommendations for prevention of squamous carcinoma: In high-risk populations, esophageal cytology, possibly supplemented by tests for blood in the stomach, appear most useful. Repeated screening may be necessary to detect early invasive or preinvasive (dysplastic) tumors. Although preliminary results from dietary intervention studies have yet to show a statistically significant decrease, if trends continue these will reach significance and may be the best overall method of cancer prevention. Measures to reduce smoking and drinking are to be encouraged, but their effectiveness is questionable. For patients who are positive on screening, endoscopy (possibly with Lugol's iodine) may provide the best indication of harboring underlying carcinoma or dysplasia. Endoscopic resection will play an increasing role in treatment. With the exception of tylosis, most other predisposing conditions are unlikely to be cost effective.