Objective: To investigate the risk factors for central lymph node metastasis (CLNM), especially the large -volume metastasis (LV-LNM, number of metastatic lymph nodes >5) in patients with cN0 papillary thyroid microcarcinoma (PTMC). 
Methods: The clinical data of 512 patients with cN0 PTMC undergoing total thyroidectomy or lobectomy plus isthmusectomy plus prophylactic central neck dissection were retrospectively analyzed, and the patients were divided into LV-LNM group and non-LV-LNM group according to the number of CLNM. The risk factors for CLNM and LV-LNM in patients with cN0 PTMC were identified.
Results: Of the 512 patients, 415 cases (81.1%) were females and 97 cases (18.9%) were males; CLNM occurred in 178 cases (34.8%) and LV-LNM was found in 21 cases (4.1%). Univariate analysis showed that sex, age, tumor size, multiple lesions, extrathyroidal invasion and BRAFV600E mutation were significantly associated with CLNM (all P<0.05); sex, multiple lesions and extrathyroidal invasion were significantly associated with LV-LNM (all P<0.05). Multivariate analysis identi?ed that males (OR=1.451, 95% CI=1.030–2.044, P=0.033), age <40 years (OR=1.720, 95% CI=1.289–2.295, P=0.000), tumor size >0.5 cm (OR=1.677, 95% CI=1.218–2.309, P=0.002), multiple lesions (OR=1.872, 95% CI=1.384–2.532, P=0.000) were risk factors for CLNM; males (OR=2.852, 95% CI=1.773–4.588, P=0.000), age <40 years (OR=1.913, 95% CI=1.434–2.552, P=0.000) and multiple lesions (OR=1.579, 95% CI=1.161–2.148, P=0.004) were risk factors for LV-LNM.
Conclusion: Sex, age, tumor size and multifocality are risk factors for CLNM in PTMC patients. Prophylactic central neck dissection should be aggressively performed in males and those with age <40 years or multiple lesions, because these patients may be more prone to LV-LNM.