Symptoms of hypothyroidism are often unspecific and numerous. As a doctor you will not get the diagnosis if you do not think of the disease and take the tests necessary to verify it. Doctors have been criticised for not being able to make the correct diagnosis and give proper treatment to these patients. As a consequence, too many patients are treated. Here we describe four patients who illustrate how conventional radiotherapy after cancer mammae surgery gave rise to hypothyroidism, how fine needle aspiration biopsy of the thyroid gland can help in the diagnosis of autoimmune thyroiditis, and a patient without hypothyroidism who was treated with thyroxine and triiodothyronine.