Background. Endocrine comorbidity, a concomitant radiation injury of several endocrine glands, is a topical issue in radiation medicine. The purpose of the study was to establish a correlation of secondary hyperparathyroidism with thyroid and pancreatic disorders among the Chornobyl nuclear power plant (NPP) accident survivors. Materials and methods. A blind sample (n = 60) of subjects treated at the radiation endocrinology department in 2019 was selected for the study. Study sample included the Chornobyl NPP accident survivors (group 1, n = 40) and patients not exposed to radiation (group 2, n = 20). The average age of people was 60.2 ± 9.8 years. Decompensation of type 2 diabetes was the most common cause for hospital admission (48.3 %), decompensation of hypothyroidism was in second place (46.7 %). Research methods: clinical, instrumental, laboratory, statistical. Results. Incidence of the increased risk of vitamin D deficiency and excessive parathyroid hormone production in the Chornobyl NPP accident survivors was somewhat higher than in individuals not exposed to radiation (81.08 and 78.12 %; χ2 = 0.257, p = 0.612; 31.12 and 28.08 %; χ2 = 0.462, p = 0.319, respectively). Using a multivariate analysis, the reliable model was obtained confirming the relationship of increased parathyroid hormone level and early subclinical signs of the target organ damage (F = 4.294; p = 0.042), which proves the relevance of using clinical questionnaires. A reliable positive correlation was found between the vitamin D and free thyroxine levels (r = 0.729; p = 0.001), and negative one was found with the thyroid-stimulating hormone content (r = –0.803; p = 0.001). In the Chornobyl NPP accident survivors with type 2 diabetes, a decreased vitamin D concentration correlated with an increased duration of metformin therapy (r = –0.421; p = 0.001) and body mass index (r = –0.787; p = 0.001). It was found that the parathyroid hormone level increases along with the duration of type 2 diabetes and an increase in creatinine clearance (r = 0.724; p = 0.001, and r = 0.799; p = 0.001). Conclusions. Vitamin D deficiency has a negative effect on the course of comorbid disorders (type 2 diabetes and hypothyroidism) and excessive production of parathyroid hormone.