The assessment of mandibular invasion is an important part of the pre-operative staging of oropharyngeal squamous cell carcinoma. When bone is surgically resected, histology often shows no direct bone invasion, yet such resections are associated with post-operative complication and morbidity. This prospective study of a large group of patients aims to lay down criteria for bone invasion using radionuclide bone imaging and orthopantomography, and to test their effectiveness when compared with histological analysis. 77 patients with proven squamous cell carcinoma of the oral cavity were investigated pre-operatively by radionuclide bone imaging and orthopantomography. All had bone resected as part of complete resection of the tumour. One patient had systemic bone metastases and was, therefore, excluded. In the remaining 76 patients, there were four false positive assessments for bone invasion radiologically and no false negatives. There were 48 true positive results and 24 true negatives, giving a sensitivity of 100% and specificity of 86%. It is concluded that correct application of the outlined criteria for bone invasion demonstrated that radionuclide bone imaging and orthopantomography are a sensitive test for bone invasion, with an acceptable level of specificity.