In patients with Graves' orbitopathy (GO), magnetic resonance imaging (MRI) is a valuable tool to distinguish the acute inflammatory active disease from fibrotic, inactive end stage disease in demonstrating interstitial oedema within the extraocular muscles on coronal TIRM-sequences. MRI is the modality of choice to identify active inflammatory changes and to assess any immunomodulatory treatment response. MRI is always required in doubtful cases, as e.g., asymmetrical orbital involvement, to exclude any other orbital pathology and the clinical suspicion of dysthyroid optic nerve compression in Graves' orbitopathy. Computed tomography (CT) provides precise imaging of the osseous periorbital structures, but does not reveal information on the disease activity in most cases. It is therefore the method of choice to plan CT-guided orbital decompression surgery in the inactive phase of GO.