Autoimmune thyroid diseases are characterized by immune dysregulation and chronic inflammation mediated by cytokine networks. Interleukin-23 (IL-23) is a pro-inflammatory cytokine that plays a key role in the differentiation and maintenance of T helper 17 (Th17) cells, which are involved in autoimmune responses. The present study aimed to evaluate serum IL-23 levels in patients with hypothyroidism (HYPO), hyperthyroidism (HYPER), and healthy controls. Serum IL-23 concentrations were measured using a quantitative sandwich enzyme-linked immunosorbent assay (ELISA). The results showed that the mean IL-23 levels were 15.33 ± 8.95 pg/mL in the HYPO group, 26.95 ± 23.28 pg/mL in the HYPER group, and 21.43 ± 11.39 pg/mL in the control group. Statistical analysis using one-way ANOVA revealed a significant difference among the study groups (F = 4.803, P = 0.011). Post hoc Tukey analysis demonstrated a significant increase in IL-23 levels in the hyperthyroid group compared with the hypothyroid group, while no significant differences were observed between the control group and either patient group. These findings suggest that IL-23 may contribute to immune activation associated with hyperthyroidism and may play a role in the immunopathogenesis of thyroid disorders. The IL-23/Th17 axis could therefore represent a potential biomarker and therapeutic target in autoimmune thyroid diseases.