This study assesses the role of orthopantomography, computerized tomography and intra-operative assessment in predicting the presence and extent of mandibular invasion by mouth tumours. Forty patient's with squamous carcinoma of the oral cavity and oropharynx were studied. All had pre-operative orthopantomography and computerized tomography as well as intra-operative assessment of mandibular invasion and these factors were compared with the actual histological invasion to assess the role of each test. This study found that negative radiology is useful for excluding cortical invasion and as might be expected is of no real value in excluding periosteal invasion, a positive orthopantomogram accurately predicts invasion at least into the cortex, however, a positive CT must be judged cautiously due to false positives and intra-operative assessment by an experienced operator is a useful adjunct to radiology.