The study aims were to characterize patients with papillary thyroid microcarcinoma (PTM) and to provide data on long-term outcome. About 900 patients with PTM (tumor size 1 cm or less) had treatment at our centre during 19452004. Follow-up extended to 54 years. Mean follow-up for 638 survivors was 13.5 years. Recurrence and mortality details were derived from a computerized database. Median tumour size was 7 mm. About 99% of tumors were grade 1; 98% were not locally invasive. About 30% of patients had nodal metastases at presentation. Three (0.3%) had distant spread at diagnosis. About 85% underwent bilateral lobar resection; regional nodes were removed by either node picking (27%) or an appropriate compartmental dissection (33%). Tumor resection was incomplete in five cases (0.6%). Radioiodine remnant ablation (RRA) was performed in 155 patients (17%). All-causes survival did not differ from expected (P=0.08); three patients (0.3%), to date, have died of PTM. None of 892 patients with initial complete tumor resection had distant spread during 20 postoperative years. No localized tumor in a female patient was fatal, and no male patient died of PTM in the first 30 postoperative years. Twenty-year and 40-year tumour recurrence rates were 6% and 9%. About 81% of postoperative recurrences have been in regional neck nodes. Higher recurrence rates were seen with multicentric tumors (P=0.002) and node-positive patients (P<0.001), but not after unilateral lobectomy (P=0.49). Tumor recurrence rates did not appear to be significantly improved by RRA (P=0.093). These results reaffirm that papillary microcarcinoma has an excellent prognosis, if primary tumor is completely resected. More than 99% of PTM patients are not threatened by the risks of distant spread or cancer mortality. Neither the performance of a total thyroidectomy, nor the administration of postoperative RRA, improved outcome during 40 years, in terms of either tumor recurrence or cause-specific mortality.