Graves disease is an organ-specific autoimmune disorder characterized by variable clinical and laboratory patterns and by alternating remissions and relapses. We investigated if a correlation exists between the hypervascular pattern of Graves disease, studied with color Doppler US (CDUS), and the degree of thyroid hyperfunction, estimated according to biohumoral parameters. We also investigated if CDUS can differentiate, with the help of pathologic correlations, the glandular histologic patterns recently reported in the literature in thyroidectomized patients. Forty-five patients with Graves disease were selected and submitted, in the same day, to CDUS and to a clinical biohumoral test, including hormone and antibody assays. Eight of these patients had undergone total thyroidectomy. The following variables were studied in each patient: US structure and glandular thickness, color spot distribution, VP, R1, T3, T4, TRab, Tmab, Tgab and patient's age. Thirty-three normal volunteers were also examined. CDUS demonstrated two patterns: pattern A consisted in many homogeneous and bilobed color spots all over the glandular structure; pattern B consisted in color spots areas and/or vascular bands surrounding avascular areas. Pattern A was seen in 13/45 patients (28.9%) and pattern B in 32/45 (71.1%). The subdivision into two groups showed significant differences from a statistical point of view (0.05 > p > 0.001) in relation to the following indices: Vp, T3 and gland size. Of the 8 patients submitted to total thyroidectomy, 3 had pattern A and 5 had pattern B at CDUS. Histology showed major differences between the two groups: thus, thyroidectomized patients with pattern B had thickened interlobular septa and more nodules. with reduced vascular component. Our study confirms that CDUS can diagnose hyperthyroidism; moreover, this technique seems to be capable of differentiating, with the help of color and flow velocity analyses, two different abnormal patterns, which we called A and B. The early results of this preliminary study seem to indicate that CDUS can show two distinct patterns of Graves disease, which differ from a histologic viewpoint and probably also in clinical aggressiveness.