There have been many reports about the usefulness of CT in diagnosing cervical lymph node metastasis from oral cancer. With relatively high diagnostic accuracy, various diagnostic criteria have been used. This study evaluated CT images of cervical lymph node metastasis in patients with oral cancer using these criteria. Eighty-nine cases of various oral cancers (132lymph node groups) were evaluated regarding cervical lymph node metastasis. In patients with nodes measuring over 1cm in minimal axial diameter, 58.1% were metastatic (metastatic/total=47/74), while 17.2% of patients with nodes measuring less than 1cm in minimal axial diameter of lymph node were metastatic (10/58). As for other diagnostic criteria, in patients with spherical nodes, 38.7% (metastatic/total=29/75), in patients showing ring enhancement, 70.4 % (19/27) and in patients with fusion, 75.0% (3/4) were metastatic. In addition, in patients with spherical nodes measuring over 1cm in minimal axial diameter, 59.5% (22/37), in patients with nodes measuring over 1cm in minimal axial diameter and showing ring enhancement, 78.3% (18/23), in patients with spherical nodes showing ring enhancement, 60.0% (9/15) and in patients with spherical nodes measuring over 1cm in minimal axial diameter and showing ring enhancement, 64.3% (9/14) were metastatic. In case of disappearance of fat layer (1/1), cancer infiltration of the surrounding tissue was seen. In conclusion, over 1cm in minimal axial diameter, spherical node and ring enhancement were found to be appropriate diagnostic criteria. Furthermore, CT is essential in diagnosing cervical lymph node metastasis from oral cancer.