106 patients, 114 W, 27 M, were thyroidectomized for differentiated thyroid cancer (follicular 29.3 % - papillary 54.3 %) with different stages of gravity (NO: 48.2 % - N1: 32.8 % - N2: 19 %). Neck dissection was used in cases of involved nodes. One or several doses of 131 I were given to 126 subjects, 106 patients were treated with LT4 (mean daily dose: 2.5 mu g/kg BW). 23 patients presenting intolerance to LT4 with non suppressed TSH for 13 of them were treated by an association of TRIAC + LT4. The follow up included a yearly check up involving clinical examination, plasma Tg and TSH assessment, neck ultrasonography and X ray of the chest. Therapy was stopped for 4 weeks in cases with Tg above its detectable value and a total body scan performed with Tg and TSH controls. The mean duration of follow up was 94.5 +/- 67.7 months and extended to more than 5 years for 61 % of the patients. We observed 22 relapses of the tumor with 4 deaths. Age less then 45 years, appears as the best factor of prognosis. 2 groups of patients were compared to evaluate the incidence of TSH suppression on the relapse free survival (group 1 n = 30 with a TSH less than or equal to 0.10 mU/1 and group 2 n = 15 with a TSH always > 1 mU/1 during the follow up). The relapse free survival was shorter in group 2 (p = 0.01). Association of TRIAC with LT4 leads to a reduction of the daily dose of LT4 (m = 25 mu g/day) with a significant improvement of TSH suppression and clinical tolerance. In conclusion, TSH suppression improves the prognosis in thyroidectomized patients for differenciated carcinoma. Association of TRIAC with LT4 seems able to improve TSH suppression and therapeutic tolerance.