A 42-year-old man presented with a 3 day history of drooping of the right eyelid and intermittent double vision. He was found to have mechanical restriction of the left eye in elevation and MRI demonstrated an abnormality in the left maxillary sinus with descent of the left inferior rectus muscle. CT confirmed the diagnosis of 'imploding antrum' or 'silent sinus' syndrome. It was treated surgically with complete resolution of symptoms and signs.