Abnormalities of the thyroid gland and of some adjacent structures arouse interest because of their surgical implications. One need only think of a non-recurrent laryngeal nerve, of thyroid hemiagenesis or of a quadrilobate thyroid gland, as in the case described here. To the best of the authors' knowledge, no similar reports of such a case are present in the medical literature. The patient was a 37-year-old woman suffering from Graves' disease. The abnormality was detected only during surgical examination and consisted in two lobes divided by a cleft on each side and joined by an isthmus. After a number of considerations regarding the anatomical details of this case and a review of the literature, the authors attempt to give an embryological interpretation and formulate the hypothesis that the second lateral lobe could be a development of the widely studied and controversial embryological anlage, the so-called "lateral thyroid".