Magnetic resonance (MR) imaging of jugular venous thrombosis was investigated in three patients who had symptoms suggestive of this condition; the diagnosis was later confirmed by computed tomography, by venography, and clinically. Bright intraluminal signal intensity was seen throughout the course of the affected jugular vein on MR images in all three patients, in sharp contrast to the lack of signal from the corresponding site in the uninvolved venous system. Temporal changes in signal intensity from the acute to subacute stage of thrombosis were evaluated for one patient. A relative increase in signal intensity for the subacute phase was believed to be related to a decrease in the T1 relaxation time. MR may be the imaging modality of choice in the investigation of venous thrombosis.