Ninety-eight patients with differentiated thyroid carcinoma were studied. Actuarial methods were used to investigate the 10-yr probability of survival (pS) and disease-free survival (pDFS). Our results show that the pDFS is a function of:(1) clinicopathologic stage: Stages I-II, pDFS= 90.9% ___ 5.0% versus Stages Ill-IV, pDFS= 55.9% ___ 17.8%(p< 0.005);(2) age: Age< 45 yr, pDFS= 87.2% _+ 10.0% versus age ___ 45 yr, pDFS= 66.6% ___ 12.0%(p< 0.002); and (3) plasma thyroglobulin (Tg) levels: Tg _< 23 ng/ml, pDFS= 100% versus Tg> 23 ng/ml, pDFS= 68.3%--10.6%(p< 0.005). Using the multivariate analysis of proportional risk, the regression coefficients obtained (Stage:/3= 0.7615; Age:/~= 1.6398, and Tg:~= 1.7607) allowed us to establish two different groups of risk of relapse on the basis of a prognostic index.