Patients with serious inflammatory Graves' ophthalmopathy should be treated with anti-inflammatory drugs or radiotherapy to prevent complications like fibrosis, while those with non-inflammatory ophthalmopathy may be treated by surgery immediately. It is often difficult, however, to distinguish inflammatory from non-inflammatory Graves' disease. We therefore present a simple clinical classification here to differentiate between these two conditions. This classification is based on the classical signs of inflammation--pain, redness, swelling, and impaired function. After two consecutive clinical examinations an 'activity score' can be determined, ranging from 0 to 10 points. In a retrospective study testing the efficacy of this classification we found that patients with an activity score of 3 or more at the beginning of therapy responded well to anti-inflammatory drugs, while those with a lower activity score mostly did not. Comparing the pretreatment activity score with the degree of enlargement of the extraocular muscles on the CT scan, we found a significant correlation between these two parameters: the higher the activity score, the more the enlargement of the muscles. We conclude that this classification facilitates the proper selection of patients for treatment.