A case of isolated unilateral extraocular muscle myositis following an acute upper respiratory tract infection is reported. Painful eye movements, restricted eye motility and exophthalmus but a normal visual acuity are the most important clinical findings. High resolution contrast enhanced CT and MRI are the imaging modalities of choice to differentiate from other orbital pathologies. The solitary enlarged muscle was clearly seen on both the contrast enhanced CT and the MR examination. Preseptal cellulitis was better seen on MRI, whereas high resolution CT was superior in the demonstration of periscleritis. Graves' ophthalmopathy and orbital cellulitis first have to be excluded. Corticosteroids are the therapy of choice in orbital myositis. A control, contrast enhanced CT after 4 weeks showed an almost normal muscle.