The relationship between the mode of tumor invasion in the tumor-host borderline and the frequency of regional lymph node metastasis was investigated in squamous cell carcinoma of the oral cavity. Cases with grades 1-3 mode of invasion classified by modified Jacobsson criteria showed a low frequency of metastasis (10/72, 13.9%), while those cases with grade 4 mode of invasion, which consisted of grade 4C (cord-like type) and grade 4D (diffuse type) showed a high frequency of metastasis (4C:11/18,61.1%; 4D :9/12,75.0%; total 20/30,66.7%). Moreover, the number of metastatic nodes in each case of mode of invasion ranged from 1 to 3 in grades 1-3, from 1 to 5 in grade 4C, and from 1 to 7 in grade 4D . The presence of metastasis indicated a poorer prognosis than did the absence of the mode of invasion in each grade, especially in grades 4C and 4D .