Twenty-five patients (48 eyes) underwent transantral, surgical decompression of their orbits for treatment of Graves' ophthalmopathy with optic neuropathy. Visual acuity improved in 77%, remained unchanged in 17%, and worsened in 6%. Colour vision improved in 76%, remained unchanged in 20%, and worsened in 4%. Visual fields improved in 67%, remained unchanged in 12%, and worsened in 22%. In general the worse the vision preoperatively the greater the relative improvement postoperatively. Clinical and radiological findings failed to correlate with visual outcome of surgical intervention. The study shows surgery to be highly effective in restoring optic nerve function for patients with severe Graves' ophthalmopathy.