The aim of the present work was to study the relationship between thyroid low echogenicity, the thyroid blood flow by color-Doppler (CD) and histological features in patients with Graves' disease (GD). Thyroid ultrasonography and CD was performed on 28 patients with GD. In 5 patients has been compared CD with histology. The thyroid volume was higher in 100% of patients with GD at the onset rather than in euthyroidism. Diffuse hypoechogenicity of the thyroid was discovered in 100% of patients with GD at the onset and it persisted in 57.1% of patients that became euthyroid after therapy. Qualitative CD resulted in different patterns that were classified as follow: pattern A ("thyroid inferno") in 17 patients (60.7%); pattern B (mildly increased of parenchymal blood flow) in 11 patients (39.3%). In the 5 histological proven cases, in the pattern A (3 cases) there was a diffuse microfollicular hyperplasia with functional activation notes. There was lymphocytic infiltration. While in the pattern B (two cases) there were a non-follicular hypercellular nodule with pseudocapsule and rare colloid. We conclude that there are two different histological types with different CD patterns in GD.