Recent molecular pathology studies in head and neck cancer support a carcinogenesis model in which the development of a field with genetically altered cells plays a central role. This preneoplastic field is of monoclonal origin and expands non-invasively superseding normal epithelium. Clonal divergence and selection within the field ultimately leads to the development of cancer. These fields can be large (over 7 cm diameter) and are often not visible for the surgeon explaining that they may remain after resection of the primary tumor. When not removed, a field is an important risk factor for secondary cancer.