Tumour thrombus is the presence of tumour cells in great vessels. The reported incidence of tumour thrombus in thyroid carcinoma is about 0.2-3.8%. Being asymptomatic, detection of tumour thrombosis clinically is difficult. We present the report of internal jugular vein (IJV) tumour thrombosis in a known follicular thyroid carcinoma patient, detected with multimodality imaging. Grayscale ultrasound scan of the neck showed a well-defined, bi-lobed (2.4 x 1.5) cm, intraluminal solid lesion with homogeneous echotexture within the distal left IJV close to its confluence with the ipsilateral subclavian vein. The lesion showed significant internal vascularity on colour Doppler assessment. The sonographic findings confirmed further imaging with computed tomography (CT) and radioisotope scans. We con-clude that patients with thyroid cancer should be evaluated for tumour thrombosis both clinically and with imaging, particularly with ultrasound and CT/MRI or nuclear medicine, as it has prognostic implications.