Disorders of lipid metabolism in endocrine diseases are a frequent occurrence in the daily practice of a doctor and usually have secondary nature. In thyrotoxicosis they have normal or decreased level of total cholesterol and low-density lipoproteins. A clinical case of a patient with thyrotoxicosis, hypercholesterolemia and hypertriglyceridemia is presented. The clinical and laboratory results of the study of the child and his parents are presented. DNA testing was conducted to clarify the diagnosis and conduct differential diagnosis of dyslipidemia type. This case shows difficulties in the diagnostic search for the etiology of dyslipidemia and its correction.