Prognostic factors and therapeutic results in a group of 268 patients with differentiated thyroid cancer (DTC) aged over 60 years are reported. These cases were selected from a total of 1457 DTC-patients seen at our Center from 1967 to 1987. All elderly patients underwent total thyroidectomy, and were treated with 131I therapy and suppressive hormonal therapy. Moreover, external radiotherapy was performed in 20% and chemotherapy in 3.8% of all cases. Follow-up included periodical clinical examination, serum Thyroglobulin (Tg) determination, 131I total body scan (TBS), and echographic and radiologic survey. Several unfavorable prognostic factors were identified in elderly patients with DTC. In comparison with data obtained in a group of patients under 60 years of age, 1) the follicular histologic type was increased, papillary/follicular ratio was 1.1 vs 2.6; 2) the F/M ratio was decreased, 1.5 vs 2.8 for papillary tumors, and 1.7 vs 3.6 for follicular tumors; 3) the rate of cases with local extrathyroid tumor growth and distant metastases was higher, and 4) rates of metastases to bone and metastases with low 131I uptake were increased. Moreover, the 10-year survival rate in elderly patients with lymph node and distant metastases was significantly reduced compared to younger patients, both for papillary and follicular cancer. The finding of detectable serum Tg levels was well correlated with the presence of metastatic disease. Moreover, Tg sensitivity was higher than TBS in showing the presence of metastatic foci. DTC in elderly people must be considered an aggressive tumor both for follicular and papillary histologic types. A radical approach is recommended: total thyroidectomy, 131I administration, and suppressive hormonal therapy.(ABSTRACT TRUNCATED AT 250 WORDS)