Histologic analysis of squamous cell carcinoma of the lower alveolus shows 2 basic patterns of tumor spread in relation to the mandible: an infiltrative one and an expansive one. While the tumor invades the mandible by destroying the bone or through cortical defects of some spaces in the infiltrative form, the tumor does this only by eroding the bone in the expansive form, in which the degree of bone resorption seems to be proportional to tumor advancement. A comparison between radiologic and histologic features discloses that the radiologically detected bone defects are not necessarily correlated with the patterns of bone involvement. However, most lesions with erosive bone defects show the expansive pattern histologically, and the extent of the radiologically detected bone defect is roughly in accordance with the histologic extent of bone involvement. These results lead us to believe that some squamous carcinoma of the lower alveolus could be treated successfully without sacrificing the continuity of the mandible.