Graves' disease is the most common form of hyperthyroidism, accounting for 60-80% of all cases of thyrotoxicosis. If left untreated, it may lead to severe thyrotoxicosis with cardiovascular, ocular, psychiatric complication, and in extreme cases thyrotoxic crisis with a high mortality rate. We present the case of a 50-years-old woman diagnosed in another service with Graves' disease and treated for many years with antithyroid drugs (ATDs), admitted to our service for a relapse due to treatment discontinuation. The surgical treatment was planned and the preoperative preparation with Lugol solution was initiated. Due to a misunderstanding, the administration of iodine solution was extended for a period of about 30 days, thus generating the so-called Jod-Basedow effect, with the exacerbation of the manifestations of thyrotoxicosis and risk of thyroid storm. The patient received treatment with high ATDs doses, glucocorticoids, and beta-blockers, resulting in the progressive improvement of symptoms. She was discharged from hospital and given the risk of thyrotoxic crisis the surgery was postponed. After a month, the patient underwent thyroidectomy without preoperative preparation with iodine solution. The operative and postoperative courses were uneventful.