The recent prevalence of ultrasonography has made it easier to detect lymph node metastasis in the lateral compartment of patients with thyroid carcinoma. In this study, we investigated the prognostic impact of lateral node metastasis preoperatively detectable by ultrasonography (US) and metastasis diagnosed by pathology examination but not detected on preoperative US [anatomopathologically (AP)-detectable metastasis] in 560 patients with papillary carcinoma >1 cm in diameter, who underwent thyroidectomy with modified radical neck dissection at our hospital. Patients with US-detectable metastasis (US+ patients) showed a significantly worse relapse-free survival (RFS) rate than those with no metastasis (US-/AP- patients) or AP-detectable metastasis (US-/AP+ patients) regardless of tumor size. Furthermore, the RFS of US-/AP+ patients with tumors >2 cm was worse than that of US-/AP- patients with tumors >2 cm or US-/AP+ patients with tumors measuring 1.1-2.0 cm. There was no significant difference in RFS between US-/AP+ and US-/AP- patients with tumors measuring 1.1-2.0 cm. These findings suggest that US-detectable lateral metastasis predicts a worse RFS for patients regardless of tumor size, and AP-detectable metastasis affects the RFS of patients with tumors >2 cm.