Clinical, laboratory, and scintigraphic findings, and magnetic resonance (MR) images of three patients with subacute thyroiditis are presented in all three at the time of diagnosis. On T1-weighted images, regions of abnormality with irregular margins and slightly high intensity were demonstrated. On T2-weighted images, markedly increased intensity was shown in the same sites. On follow-up MRI in two patients after treatment, these findings had disappeared or become more normal.