- Hypothyroidism (HPO) in humans is widely believed to impair health. The biochemical factors mediating decline in health, however, are poorly elucidated. Pathological consequences of HPO point to a high potential for antioxidant imbalance. The objectives of this study were to investigate the major antioxidants in persons with intellectual disability (ID) and HPO in order to find the effect of chronic disease on the level of antioxidative parameters. This is a prospective, nonrandomized study. A total of 11 people with HPO and 11 age-matched healthy participants were examined. The following antioxidative defense were examined: superoxide dismutase (SOD), catalase, glutathione peroxidase (GSH-Px), and glutathione reductase (GR) as well as two biochemical parameters creatinine and albumin. Compared to healthy control subjects without complications, persons with ID and HOP had significantly lower SOD (p < 0.05), catalase (p < 0.05), GSH-Px (p < 0.05), except the GR level (p = NS). A significant correlation was found between age and gender and AO values in experimental group SOD (r = −0.882), catalase (r = −0.724) and GSH-Px (r = −0.782). Our preliminary results confirm the hypothesis that there is a reduction of the antioxidative defense in persons with HPO and in particularly among males.