Hypothyroidism commonly occurs after both radioiodineand surgical treatment of thyrotoxicosis. Since the incidence increases with the passage of time, it is important to follow all such patients for life. A system is presented which makes use of clinical judgement and the measured Achilles’ reflex time. In persons with easily reproducible reflexes this combination may be used to assure the continued euthyroid state after it has been reached, to suggest the presence of hypothyroidism, and to verify the hypothyroidism once suspected. Application of the method may help to reduce the large pool of patients with post-treatment hypothyroidism.