The cyclin D1 oncogene is critical in the progression of the cell cycle through the G1 phase. It is frequently overexpressed in squamous cell carcinomas originating from the head/neck and esophagus. Yet, the functional consequences of aberrant cyclin D1 overexpression are not entirely understood apart from increased cell proliferation. To address this question, we have developed a transgenic mouse model in which the EBV ED-L2 promoter targets cyclin D1 to the stratified squamous epithelium in a tissue-specific fashion to the tongue and esophagus, thereby resulting in a dysplastic phenotype. We now demonstrate that the dysplastic phenotype is associated with increased cell proliferation based on proliferating cell nuclear antigen overexpression and abnormalities in cyclin-dependent kinase 4, epidermal growth factor receptor, and p53. In aggregate, these studies suggest that alterations in certain oncogenes and tumor suppressor genes occur early during head/neck and esophageal carcinogenesis.