Background <p>Selenium is an essential trace element, and its deficiency is associated with thyroid dysfunction, which is known as a cardiovascular risk factor. Hemodialysis (HD) patients are particularly prone to selenium deficiency, and this nutritional factor may increase the risk of thyroid dysfunction and subsequently cardiovascular disease (CVD). Therefore, we investigated selenium deficiency in HD patients and tried to analyze the effect of selenium deficiency on thyroid dysfunction and its correlation with CVD.</p> Methods <p>A cross-sectional study was conducted with 183 chronic HD patients. Selenium deficiency was defined as a serum selenium level below 90&#xa0;µg/L. Patients were categorized into subgroups based on selenium status and/or thyroid hormone dysfunction. CVD prevalence was assessed.</p> Results <p>Of the 183 subjects, 79 (43.2%) had selenium deficiency, which was associated with a trend toward higher thyroid dysfunction and increased CVD. In the subgroup analysis, the group with both selenium deficiency and thyroid dysfunction showed a significantly higher CVD prevalence of 68.1% compared to other groups. Additionally, in the logistic regression analysis for CVD risk factors, selenium deficiency/thyroid dysfunction was found to have a significant odds ratio of 3.171.</p> Conclusions <p>This study demonstrates that selenium deficiency is associated with thyroid dysfunction and an increased CVD risk in chronic HD patients. Moreover, a negative synergistic effect on CVD was observed when both selenium deficiency and thyroid dysfunction were present.</p>