Thyroid cancer occurs in 3—18.3% of patients with nodular and multinodular toxic goiter. It is usually represented by papillary carcinomas <1 cm, while medullary cancer accounts for less than 5% of all thyroid malignancies and is rare with hyperthyroidism. This paper aims to substantiate a complex examination for senile patients with nodular/multinodular toxic goiter to exclude malignancies. The paper describes a clinical case of a 72-year-old woman with nodular formations in the thyroid gland established in 2014, with no dynamic follow-up. An examination at the Endocrinology Research Center in 2021 revealed anatomical abnormalities of the thyroid gland and toxic multinodular goiter. A formation found in the paratracheal region was assessed as lymph node metastasis of C-cell carcinoma based on fine-needle aspiration biopsy. The patient underwent surgical treatment, including extra fascial thyroidectomy with central lymphadenectomy. Histological and IHC examinations revealed a medullary carcinoma with multifocal growth pattern pT1a(m)NxMx R0 Pn0 LV0, a noninvasive follicular tumor with papillary nuclei, and multinodular goiter. The presented case evidences possible diagnostic bias in anatomical abnormalities of the thyroid gland, such as an aplasia of the right lobe and formation of the pyramidal lobe, and the need for dynamic follow-up of patients to prevent thyrotoxicosis.