The study aimed to investigate the effectiveness of the vascularization index (VI) obtained using superb microvascular imaging (SMI) technique in the diagnosis of Hashimoto thyroiditis (HT). The thyroid glands of 80 patients with HT and 107 healthy, asymptomatic participants were examined using SMI. The thyroid parenchyma echogenicity was evaluated, and the thyroid gland volume was measured. Vascularization index measurements were performed by manually drawing the contours of the thyroid parenchyma using the free region of interest with color 2-dimensional SMI VI mode. The quantitative VI values of the patients and the asymptomatic group were compared. Correlations between VI values and thyroid autoantibodies and thyroid hormone levels were analyzed. The mean VI value of the thyroid gland was 4.74% ± 1.96% in the asymptomatic group and 12.45% ± 5.87% in HT patients with a statistically significant difference (P < 0.001). Hashimoto thyroiditis can be diagnosed with 86.3% sensitivity and 82.2% specificity when 6.00% VI value was designated as the cutoff value. There was a positive significant correlation between the VI value and the thyroid-stimulating hormone, antithyroglobulin antibodies, anti-thyroid peroxidase antibody levels (P < 0.05); however, no significant correlation was found between the VI values and thyroglobulin and free thyroxine levels (P > 0.05). There was a significant negative correlation between the VI values and the parenchyma echogenicity and positive significant correlation between the thyroid gland volume and the antithyroglobulin antibody and anti-thyroid peroxidase antibody levels (P < 0.05). The VI obtained using the SMI technique can be effectively used as an imaging method for the diagnosis of HT because of its high sensitivity and specificity in representing objective, quantitative numerical values.