The role of the lingual periosteum in the spread of tumours is not yet clear. We examined the histological behaviour of 60 cancers of the tongue and floor of the mouth lying close to the mandible. There were no tumour cells in the periosteal lymphatics. This is in accord with clinical experience that tumour invasion of the periosteum is not associated with an increased rate of metastases to the cervical lymph nodes. From our experience, we conclude that (1) a radical resection of the mandible is mandatory for every lesion lying in the gingivo-lingual gutter that invades bone; (2) for tumours close to, but not directly invading the lingual surface of the mandible, marginal resection of the alveolar ridge is appropriate and provides an adequate margin.