PURPOSE: A lateral neck node metastasis is common in patients with papillary thyroid carcinoma. If a preoperative diagnosis is not made or is uncertain, an intraoperative biopsy for a frozen examination should be considered. The aims of this study were to evaluate the factors predicting a lateral neck node metastasis and to suggest guidelines for an intraoperative neck node biopsy. METHODS: From March 2003 to January 2006, 79 patients (7 males, 72 females) with 89 intraoperatively biopsied lateral neck nodes were enrolled in this study. The median age was 45 years. Among these patients, two or more lateral neck nodes were biopsied intraoperatively in 9 patients and one node was biopsied in the others. The clinicopathological features and radiological findings were reviewed. RESULTS: Among the 79 patients with 89 lateral neck nodes, 25 patients with 26 lateral neck nodes (29%) showed a metastasis. Univariate analysis revealed the computed tomography (CT) findings of lateral neck nodes such as a longitudinal size >1 cm (P=0.001), postcontrast Hounsefield Unit (HU) >110 (P<0.001), presence of necrosis (P<0.001), absence of hilum (P<0.001), and irregular margin (P<0.001) were found to be significant predicting factors. The pathologic findings of tumors such as multifocality (P= 0.006), bilaterality (P=0.001), tumor size >2 cm (P=0.008), extracapsular invasion (P=0.005) had significant impact on a lateral neck node metastasis. Multivariate analysis revealed a longitudinal size >1 cm (P=0.039), postcontrast HU >110 (P<0.001), and bilaterality of the tumor (P= 0.001) with a suspiciously enlarged lateral neck node in CT to have a significant impact on node metastasis. However, bilateral tumor with lymph nodes >110 HU were the most important factors. CONCLUSION: The most significant factors influencing lateral neck node metastasis were multifocal, bilateral, large size (2 cm < or = ), extracapsular invasion of the primary tumor, and the CT findings of lymph nodes such as a large longitudinal size (1 cm < or =), necrosis, the absence of hilum, irregular margin and increased postcontrast HU (110 < or =).