Background. Differentiated thyroid cancer (DTC) is the most common endocrine tumour. Its prevalence varies from 1.0% to 2.2% of all malignant neoplasms. The standard strategy of special treatment of DTC consists of surgery, radionuclide therapy and hormone therapy being sequentially applied. Theoretically, each component of the treatment process can cause adverse somatic consequences in future, the study of which can help to prevent and correct them. Purpose – to evaluate possible long-term effects of the treatment of differentiated thyroid cancer in the form of the urinary system (US) pathologies on the basis of follow-up data of long-term observation using sophisticated information technologies. Materials and methods. The study was based on follow-up data of 157 individuals who were undergoing combination treatment of DTC at the Institute clinic from 1993 to 2015, received it in full and underwent regular screening examinations after treatment. The database created for the study contained, as much as possible, digitized arrays of follow-up data of paper case-records on the disease and its consequences in patients with a follow-up period exceeding 1 year after special treatment. The number of logical records of long-term consequences in the generated database was 463 units – one record for one type of long-term consequences of each of 157 patients. Statistical processing of data was carried out in two ways: comparing the incidence of US pathologies before treatment and at a long time after special treatment and identifying factors of statistically significant influence on the occurrence of US pathologies among the treatment peculiarities. WizWhy packages (Data Mining category) and the general purpose software package STATISTICA were used to make hypotheses and test them. Results and discussion. The analysis of the available references has shown that there is only a limited number of papers dealing with the US status of DTC patients. However, a comprehensive analysis of the long-term consequences of treatment of DTC patients revealed a statistically significant increase of US disease cases within the period of 3.75 – 4.8 years after special treatment. It was shown that the total number of US pathologies was 2.04 times higher in comparison with US incidence before the oncet of special treatment. These differences did not depend on age: the median for age of patients before treatment was 51 years, after treatment – 50 years. Additionally, it has been found that patients with or without episodes of postoperative hypothyroidism decompensation with a dose of L-thyroxine not exceeding 2.5 μg/kg need special attention due to the occurrence of urolithiasis. The obtained dependences are quite predictable, since, firstly, it is known that thyroid hormones affect kidney development and physiology, and secondly, the major percent of 131I in radioiodine therapy is excreted with the urine and deposited in the bladder, that can result in a radio-induced carcinogenic effect. Conclusions. Special treatment of DTC increases US pathologies more than twice. The term of post-treatment pathologies is 2.5 (3.75 – 4.8) years. Patients who have episodes of postoperative hypothyroidism during hormone therapy with a dose of L-thyroxine not exceeding 2.5 μg / kg represent the high-risk group.