BACKGROUND: The extent of surgery for papillary carcinoma significantly differs between western countries and Japan. Almost routine total thyroidectomy with radioiodine ablation therapy has been performed in western countries, whereas limited thyroidectomy has been adopted in Japan, especially for low-risk cases. In this study, the prognosis of patients with solitary papillary carcinoma measuring 2 cm or less without massive extrathyroid extension, clinically apparent lymph node metastasis or distant metastasis at diagnosis (T1N0M0 in the UICC TNM classification) was investigated to elucidate the appropriate extent of surgery for these patients. METHODS: We investigated the prognosis of 2,638 patients with solitary T1N0M0 papillary carcinoma who underwent initial surgery between 1987 and 2004. Total or near total thyroidectomy was performed for 1,037 patients and the remaining 1,601 patients underwent more limited thyroidectomy. Elective central node dissection was performed for 2,511 patients, accounting for 96%, and 1,545 (59%) also underwent prophylactic lateral node dissection. Radioiodine ablation therapy was performed only for three patients. RESULTS: The 10-year disease-free survival (DFS) rate of our series was 97%. To date, recurrence was observed in 62 patients (2%) and 41 showed recurrence to the regional lymph nodes. Seventeen of 1,601 patients who received limited thyroidectomy (1%) showed recurrence to the remnant thyroid. Pathological nodal-positive patients showed a worse DFS, but the 10-year DFS rate was still high at 96%. Patients with total or near total thyroidectomy had a better DFS, but the difference disappeared if recurrence to the remnant thyroid was excluded. A number needed to treat (NNT) for total or near total thyroidectomy over hemithyroidectomy was 83 to prevent 1 recurrence. CONCLUSIONS: These findings suggest that solitary T1N0M0 patients have an excellent prognosis when they undergo thyroidectomy and elective lymph node dissection without radioiodine therapy. Regarding the extent of thyroidectomy, hemithyroidectomy is adequate for these patients, if a 1% risk of recurrence to the remnant thyroid is accepted.