BACKGROUND: The indications for elective bilateral central node dissection for patients with unilateral papillary thyroid carcinoma (PTC) who are clinically node negative are still not verified. We investigated the predictive factors of lymph node metastasis and formulated guidelines for surgical extent. METHODS: From 2004 to 2009, 325 patients diagnosed with unilateral PTC who had undergone total thyroidectomy with bilateral central lymph node dissection (CLND) were enrolled retrospectively. RESULTS: Central node metastasis was found in 45.2%, ipsilateral and contralateral lymph node metastasis was found in 40.0% and 16.0%, respectively. Tumor size larger than 1.0 cm and extrathyroidal extension were significant factors in predicting ipsilateral node metastasis (p = .004, < .001, respectively), and extrathyroidal extension and ipsilateral lymph node metastasis predicted contralateral node metastasis in multivariable analysis (p = .039, < .001, respectively). CONCLUSION: Elective bilateral central node dissection may be considered in unilateral PTC with extrathyroidal extension or ipsilateral node metastasis.