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 micrograms/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 < or = 0.10 mU/l and group 2 n = 15 with a TSH always > 1 mU/l 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 micrograms/day) with a significant improvement of TSH suppression and clinical tolerance.(ABSTRACT TRUNCATED AT 250 WORDS)