This report presents a case involving a unique observation of a high-grade squamous dysplasia involving the entire esophagus.Dysplastic cells were located exclusively in the basal portion of the esophageal squamous epithelium.The findings were documented using histologic analysis of the step-biopsies from the entire esophagus,histologic examination of the esophagectomy-specimen,immunohistochemicalanalysis,and molecular pathologic analysis of the p53 gene.A minimally invasive total esophagectomy was performed at the Department of Surgery of the University of Cologne,and histologic analysis of the resection specimen confirmed extensive high-grade dysplasia involving the oral resection margin,but no invasive carcinoma.This case does not fit the current World Health Organization(WHO) definition of highgrade squamous cell dysplasia,which requires fullthickness involvement of the squamous epithelium.Thus,the WHO criteria should probably be reconsidered in order to allow for a diagnosis of high-grade dysplasia in cases where dysplastic cells are exclusively located in the basal layer of the esophageal squamous epithelium. This report presents a case involving a unique observation of a high-grade squamous dysplasia involving the entire esophagus. Dysplastic cells were located exclusively in the basal portion of the esophageal squamous epithelium. The findings were documented using histologic analysis of the step-biopsies from the entire esophagus, histologic examination of the esophagectomy-specimen, immunohistochemicalanalysis, and molecular pathologic analysis of the p53 gene. A minimally invasive total esophagectomy was performed at the Department of Surgery of the University of Cologne, and histologic analysis of the resection specimen confirmed extensive high -grade dysplasia involving the oral resection margin, but no invasive carcinoma. This case does not fit the current World Health Organization (WHO) definition of highgrade squamous cell dysplasia, which requires fullthickness involvement of the squamous epithelium.Thus, the WHO criteria should probably be reconsidered in order to allow for a diagnosis of hi gh-grade dysplasia in cases where dysplastic cells are exclusively located in the basal layer of the esophageal squamous epithelium.