The aim of our study is to compare in a randomized multicentric study the early prophylactic introduction of low dose of LT4 (50 µg/d) at 15 days post-ablation (experimental arm) compared to a conventional approach based on the initiation of LT4 as soon as the first biological signs of hypothyroidism. Two hundred patients with Graves' disease with no or minimal (eyelid retraction or oculopalpebral asynergy) and non inflammatory ophthalmopathy (clinical activity score to 0) will be included in this study. The administrated iodine-131 activity will be adjusted to the weight of the thyroid gland (20 MBq/g thyroid tissue). Patients will be evaluated at 6 weeks, 3 months, 6 months and 12 months post-ablation. The primary objective will assess differences in terms of quality of life at 3 months using a specific questionnaire (ThyPRO). Secondary objectives will compare quality of life outcomes at different study visits (using ThyPRO and SF36), fatigue (MFIS) and depression (Beck), autoimmune parameters (signs of ophthalmopathy, TSH receptor antibodies assessment), efficacy and medico-economic data.

Inclusion Criteria:

• Patient presenting a hyperthyroïdie Basedowienne proving a treatment by iodine 131.

  • Patient without or with ophtalmopathie junior defined by a score of ophtalmopathie in 0 or in 1 and a score of clinical activity in 0 (see secondary).
  • Patient whose rate of fT4 and\or of fT3 is lower than 1,5 times the superior limit of the standards of the laboratory during the balance sheet(assessment) which precedes the treatment by iodine 131 (15j.
  • Patient whose thyroïdien volume estimated by echography is lower than 60 mL.
  • Patient whose treatment by anti-thyroïdiens of synthesis was interrupted at least 5 days before the administration of iodine 131.
  • 18 years old male or feminine Patient or more.

Exclusion Criteria:

• Patient presenting a thyroïdien nodule suspect of wickedness.

  • Patient presenting disorders not thyroïdiens known to distort the fixation of I131 (congestive heart failure of class III or IV, renal insufficiency).
  • Patient having received by intravenous way a product of hydrosoluble contrast for radiography in 4 weeks preceding the randomization, or by way intra-thécale or for cholécystographie by a product of contrast iodized in three months preceding the randomization.
  • Patient taking medicines susceptible to disrupt the function thyroïdienne or renal (renal medicines, lithium, amiodarone, in particular).
  • Patient presenting a contraindication to Levothyroxine with high dose: décompensée heart disorder, coronaropathie, shady of the unchecked rhythm.
  • pregnant or breast-feeding Women, or patient being able to have children and refusing to follow a reliable contraceptive method during the duration of the study.