A case of gyrate atrophy of the choroid and retina and hyperornithinemia in a 28-year-old man was subjected to extensive clinical and biochemical investigation. The familial occurrence of the ocular disease and of abnormality of amino acids was unique to this patient, being absent in parents and siblings. He presented with progressive visual loss, and had cataracts and large areas of peripheral lacumar atrophy. Clinically there was no other abnormality. However, he was hyperuricemic and had an abnormal electroencephalogram. Despite otherwise normal biochemical indices of hepatic, renal, and muscle function, selective catheterization of an artery, the hepatic vein, the renal vein, and a deep forearm vein showed all of these circulatory beds to be producing ornithine according to arteriovenous difference measurements. Cerebrospinal fluid and urine contained increased amounts of ornithine. Though electromyography was normal a muscle biopsy specimen was abnormal. Clinical tests including arginine loading, glucose tolerance testing, and other measurements of blood variables provided inferences as to the metabolic locus of the abnormality. The syndrome is a systemic multiorgan disorder in which the choriod and retina would appear to be target organs and the hyperornithinemia to be of as yet undetermined cause and pathogenic significance.