30 patients with malignant tumours of the cavum oris and oropharynx were examined by MRI and CT to compare their accuracy for T-staging. There was histological information in all cases. Histological studies showed an accuracy in T-staging of 81% for MRI and 77% for CT. Differentiation between stages T2/T3 and T3/T4 is possible in 80% by CT and 84% by MRI. Tumours of the cavum oris and oropharynx of T1-stage are possible only in 1 of 3 cases. The use of T2-weighted sequences allows the best frequence of tumour representation in 89%. CT shows an earlier bone involvement than MRI. In addition, the ability to produce coronal and sagittal images by MRI makes it superior to CT in judging tumour extension.