Fifty-three patients with oral cavity and tongue tumors were studied with MRI, 18 with CT and 10 with US. MR results were compared with postoperative and clinical results relative to the T variable of the TNM classification of oral cavity tumors. MRI demonstrated 51 of 53 tumors; it was in agreement with surgery, relative to T, in 43 of 48 cases and with clinics in 5 of 5 cases. In 5 patients MRI understaged: two lesions were classified as T0 because the tumors developed on the surface (p T4, for alveolar ridge infiltration). Moreover, MRI staged another lesion as T2 instead of T3 because of its superficial component, while in 2 cases the infiltration of the cortical bone of the jaw was not demonstrated (T1 at MRI, T4 at p; T2 at MRI, T4 at p). MRI was reliable enough to evaluate the relationships between the lesions and the surrounding structures but it was limited in demonstrating superficial lesions and in evaluating the infiltration of the alveolar ridge and of the cortical bone of the jaw in the early stage. The use of gadolinium proved to be especially useful for the exact definition of the size of the lesions and of their relationships with the surrounding structures. CT proved better than MRI to evaluate bone involvement in one case, even though neither technique could identify bone involvement in another patient. US yielded accurate information on the presence of lesions, their size and relationships with midline and floor of the mouth muscles, while its demonstration of the relationships between tumors and bone structures was poor, especially relative to tumor spread outside the oral cavity.