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A number of seminars have shown considerable differences between Japanese and Western pathologists in the diagnostic differentiation of reactive changes, dysplasia and well-differentiated adenocarcinoma in gastroenterological biopsy material. Lesions that most Western pathologists identify as "dysplasia" are often considered adenocarcinomas in Japan. A comparison of the biopsy-based diagnoses with those established in resected mucosa, however, reveals appreciable diagnostic inexperience on the part of Western pathologists, with significant discrepancies between their diagnoses based on biopsies and those based on resected material. Against this background, a new classification of epithelial neoplasia of the gastrointestinal tract was drafted on the occasion of the World Congress of Gastroenterology in Vienna in 1998. By collapsing the diagnoses "high-grade adenoma/dysplasia, noninvasive carcinoma (carcinoma in situ), and suspected invasive carcinoma" into a single category ("noninvasive high-grade neoplasia", category 4), this scheme should largely eliminate the diagnostic discrepancies between Western and Japanese pathologists. As with every classification, the Vienna classification has its advantages and disadvantages; these are discussed here. The most important advantage of the Vienna classification is that the various categories are associated with different recommendations for further diagnostic and therapeutic measures. This applies in particular to category 4, with the recommendation for only local treatment initially (endoscopic mucosal resection or surgical excision). Since the introduction of the Vienna classification, the new World Health Organization classification of neoplasia of the gastrointestinal tract has recently been published, in which the term dysplasia has been replaced by "intraepithelial neoplasia". This means that the Vienna classification needs to be modified accordingly.