Hyperthyroidism can regularly be controlled by the administration of antithyroid drugs, and a euthyroid or hypothyroid state can be maintained for as long as treatment is continued. The optimal therapeutic schedules and the expected sequence of events during treatment have been determined.1 There remains, however, considerable divergence of opinion on the incidence of prolonged remission after cessation of a course of therapy with an antithyroid compound.2 This may in part be attributed to the many reports based on observation of patients for only a short time after the conclusion of treatment. Where this objection does not apply, the published rates of remission are nonetheless difficult to interpret, since they have been determined by giving equal weight to patients with a wide range of post-therapeutic periods of observation. This procedure introduces an obvious source of error into the data and also makes it impossible to derive the incidence of