A 16-year-old white girl presented in April 1996 with persistent diplopia in upgaze. Orbital disease had begun 6 years earlier in January 1990 with loss of motility predominantly of the left eye, painful diplopia, eyelid swelling, tearing, and burning and redness of the left eye. The patient reported that her eyes had been prominent at that time. Her vision was perfectly normal. She was treated with prednisone, which produced an improvement of the orbitopathy over the following weeks. After the dosage of prednisone therapy was lowered, conjunctival injection, swelling of the left eyelid, and diplopia resumed. Treatment with higher doses of prednisone led to a rapid improvement of the symptoms. Although systemic steroid therapy was continued afterward at a dosage of 20 mg/d, 3 other episodes involving diplopia, proptosis, and soft tissue signs occurred mainly involving the left orbit. Notably, each of the exacerbations occurred in the winter of the respective years (January 1993; February 1994, with involvement of the right eye; and January 1995). Over the years, the patient's double vision became permanent. On examination in April 1996, she had diplopia in upgaze and lateral gaze to the left side; gaze to the right was also mildly limited. Hertel exophthalmometry measurements were 14 mm on the right and 15 mm on the left. There was no history of thyroid disease, and, on examination, there were no clinical signs or symptoms of hyperthyroidism. The thyroid was normal in size and consistence, and the results of sonography of the thyroid were normal. The following laboratory investigations revealed no abnormalities: complete blood cell count; determination of serum urea nitrogen, electrolyte, creatine kinase, complement, C-reactive protein, immunoglobulin fraction, and blood glucose levels; liver function tests; Westergren sedimentation rate; serum protein electrophoresis; and serologic testing for acetylcholine receptor antibody. Serum levels of free triiodothyronine, free thyroxine, thyrotropin, thyrotropin receptor antibodies, and thyroid stimulating antibody were normal, as were the results of antimicrosomal and antithyroglobulin studies and a protirelin stimulation test.