The spread of tumour cells to the mandible has been well recognised and invasion of the edentulous alveolar ridge by tumour through accessory foramina has been documented. Tumour infiltration can also occur through the lateral cortical plate, but the number and distribution of accessory foramina on this surface has not been reported. Lateral surfaces of 89 mandibles were examined and accessory foramina which showed a direct communication with the underlying cancellous bone were charted. It was found that the number of accessory foramina varied greatly from specimen to specimen. Only 70.8% of mandibles showed foramina in the coronoid, sigmoid and condylar sections; of these 93.7% exhibited foramina in the condylar section, 23.8% in the coronoid and only 19% in the sigmoid section. This finding confirms that the current practice of conserving part of the ascending ramus posterior to the coronoid process following surgery is sound. Similarly in the rest of the lateral surface, foramina were present in the upper third section in 97.8% of mandibles, 61.8% in the lower third and 58.4% in the middle third sections. This result justifies the principle of rim resection in appropriate cases and the recognition that the alveolar section is commonly invaded before the rest of the body. The number and distribution of foramina may be of greater significance following radiotherapy when the foramina could provide multiple direct channels for invasion of tumour cells from the lateral surface to the medulla.