In graves' disease small amounts of radioactive iodine administered repeatedly on a monthly basis depending on the progress of the disease is a method whose effectiveness we have studied on 192 cases over a period of 3 to 7 years. Relapses (4 %), failures (11 %) permanent hypothyroidism (24 % after 7 years) and the duration of the active stage have been collated with different clinical or biological parameters in order better to define the main factors that determine the course and prognosis. The size of the goitre and the presence of antithyroglobulin antibodies are among the most significant.