Cervical lymph node metastasis is the most important prognostic factor in patients with head and neck carcinoma. We retrospectively analyzed the effects of three different variables-tumor size, degree of differentiation, and depth of invasion-on the risk of neck node metastasis in 50 adults who had been treated with surgery for primary squamous cell carcinoma of the oral cavity. Primary tumor depth and other pathologic features were determined by reviewing the pathology specimens. Preoperatively, 36 of the 50 patients were clinically NO; however, occult lymph node metastasis was found in 13 of these patients (36.1%). The prevalence of neck node metastasis in patients with T1/T2 and T3/T4 category tumors was 51.5 and 58.8%, respectively. The associations between the prevalence of neck node metastasis and both the degree of differentiation and the depth of invasion were statistically significant, but there was no significant association between neck node metastasis and tumor size. We conclude that the prevalence of neck lymph node metastasis in patients with squamous cell carcinoma of the oral cavity increases as the tumor depth increases and as the degree of tumor differentiation decreases from well to poor, as has been shown in previous studies. It is interesting that tumor size, which is the most important component of the TNM system, was not significantly associated with neck node involvement.