Gyrate atrophy of the choroid and retina (GA) is an autosomal recessive chorioretinal degeneration with a 10-20-fold elevation of plasma ornithine due to deficient activity of ornithine aminotransferase. Type II fibres of the skeletal muscle are atrophic and contain tubular aggregates in electron microscopy. Deficient creatine and creatine phosphate formation have been postulated to be involved in the pathogenesis of GA. The five-year follow-up results of oral creatine supplementation in 13 patients are presented. Visual function tests and fundus photographs showed progression of GA during the treatment. The velocity of the progression varied considerably between individuals. Generally, the progression was rapid in the young patients and slow in the more advanced stages. Abnormalities in the skeletal muscle decreased or disappeared rapidly. They reappeared in the few patients who discontinued the medication. The difference in the therapeutic effect on the skeletal muscle and eye is discussed.