BACKGROUND Mandibular resections are routinely carried out for achieving a R0 resection for oral cancers. However, the need of mandibular resection to achieve this has always been questioned. The present study was carried out to define the pattern of mandibular involvement in carcinoma of the mandibular region. PATIENTS AND METHODS A total of 25 consecutive patients who had undergone mandibular resection and were found to have mandibular invasion were studied in a prospective open fashion. After decalcification the specimens were serially sectioned at 1 cm interval to identify invasion of mandibular bone. Type of invasion, route of spread and host cell reactions were also recorded. RESULTS The mandibular involvement was infiltrative in 14(56%) and erosive in 11(44%). It was cortical in 5(20%), marrow involvement was seen in 15(60%) while 5(20%) had spread through the inferior alveolar canal. Of the 25, 24(96%) lesions were located with in 1 cm of the mandible. CONCLUSION The possibility of mandibular involvement is higher in patients where tumours are located with in 1 cm of the mandible. Involvement of mandible through the canal of inferior alveolar nerve in the present study was relatively high (20%). Therefore it is recommended that before a decision is taken to preserve the mandible it should be thoroughly screened for possible involvement.