Differentiated thyroid cancer grows slowly in general. But some patients repeat recurrence and progress finally to death. To clarify the difference of their prognosis and establish the appropriate thyroid surgery, we studied 105 patients with differentiated thyroid cancer who were treated with total or subtotal thyroidectomy, excluding those with small tumors, under uniform conditions regarding thyroidectomy. There were 77 women and 28 men aged 19 to 76 years (mean 54.7 years). More than 60% (alive) were followed up for longer than 10 years. Thirty-eight (36%) patients had recurrences. There were 19 deaths. Twelve of 31 patients with locoregional recurrence died and 7 of these 12 died of locoregional control failure (neck and mediastinum). Age at first operation, tumor size, and local tumor extension increased the rate of recurrence significantly. Multivariate analysis confirmed that age, locoregional recurrence, and distant metastasis significantly affected survival. Although lymph node metastases were not a prognostic factor, for patients at high risk for recurrence who are older, and have large tumors with invasion, complete resection of cervical lymph nodes is advised to prevent local recurrence and prolong the disease-free interval. Prolongation of the disease-free interval may lead to prolonged survival time.