Nephropathy is known to occur in patients with long-standing cyanotic congenital heart disease (CCHD). In order to assess the incidence, nature and degree of the problem among such patients, discriminating urine analyses were performed in 26 patients with CCHD, with a mean age of 22 (10-42) y. Ten patients showed reduced glomerular function, six of whom also had advanced glomerulopathy. Glomerular filtration rates were below normal in half of the patients and occurred with glomerular-type proteinuria in five, with tubular-type proteinuria in one and without pathological proteinuria in four. An elevated haematocrit and duration of cyanosis were identified as the main risks factors for the development of glomerulopathy. The risk of developing glomerular lesions rose sharply during the second decade of life. Nephropathy in CCHD is common and the dominant feature is glomerular damage, which is related to the duration of cyanosis and the extent to which the haematocrit is elevated.