In a review of 460 cases of intraoral carcinoma, 21 per cent of the lesions were found to erode or invade the mandible. Of 100 carcinomas of the gingivae, 56 had extended into the mandible.The roentgenographic criteria of differentiating erosive and invasive defects of the mandible secondary to carcinoma of the gingiva are presented. The pathologic correlation, indicating that the erosive lesions are Grade I or II and the invasive lesions of higher grade malignancy, has been established.Erosive lesions may be adequately treated by radiation therapy or surgery. If surgical removal is performed, a local excision rather than hemimandibulectomy is adequate.Invasive lesions are not amenable to radiation therapy. Hemimandibulectomy is indicated for these lesions.Recognition of the roentgenographic pathlologic correlation of erosive and invasive lesions of the mandible secondary to carcinoma of the gingiva will markedly improve the cosmetic and therapeutic results in patient care.Erosive carcinoma of the mandibl...