The long term follow up of surgery in normal tension glaucoma is presented. One eye of 18 patients with bilateral progressive disease underwent fistulising surgery. Over follow up periods ranging from 2 to 7 years (50% > or = 5 years) the operated eye showed on average a 30% reduction in intraocular pressure (IOP). This was associated with a marked difference in the rate and number of retinal locations showing a progressive decline in retinal function, suggesting some protective function for lowering IOP in patients with normal tension glaucoma.