Aim: to determine thyroid vascularity in healthy subjects and patients with autoimmune thyroid disease (AITD), and assess its sensitivity and specificity for the diagnosis of AITD. Methods: High-sensitivity color flow Doppler sonography (HSCFDS) was used to estimate the thyroid intraparenchymal vascularity in 31 euthyroid patients with Hashimoto's thyroiditis (HD), 33 hypothyroid patients with HD, 13 hyperthyroid patients with Graves' disease, and in 34 healthy controls. Images obtained from the ultrasound unit were further processed with a widespread, available imaging analysis program and the predictive value of the maximum vascularity index (VI) was used for further statistical analysis. Results: Compared to healthy controls, patients with AITD had higher mean VI of both the right and the left thyroid lobe (TL) (P < 0.001). The sensitivity of left TL VI values greater than 5.57% (the best cut-off value of the Receiver Operating Characteristics-ROC curve) for the diagnosis of AITD was 80.8% and the specificity was 85.3%. Right TL VI values greater than 14.75% had 84.6% sensitivity and 86.2% specificity for the differential diagnosis among patients with HT or GD. Conclusions: Measurement of right and left TL vascularity index using HSCFDS is a high specific tool, particularly where there is a high clinical suspicion of an autoimmune process.