The long-term outcome of idiopathic IgA nephropathy (IgAN) in children was investigated with regard to clinical course and biopsy changes. All patients with biopsy-verified IgAN (diagnosed by kidney biopsy 1970-1985) at three children's clinics in Sweden were included in the study. Thirty-four (10 females, 24 males), out of a total of 72 patients, had a follow-up period of 8 years or more (10.7 +/- 1.9 years, range 8-14). After this duration of follow-up, urine abnormalities were found in 47% (group A), proteinuria in 35%, hypertension in 9%, and decreased glomerular filtration rate (GFR) in 3% of patients. However, 53% had no clinical signs of disease (group B). GFR depression at the time of clinical presentation of IgAN was more common in group A than in group B (P = 0.017). At the first renal biopsy, which was performed after the same duration of IgAN in both groups, focal segmental glomerular changes were more often found in group A (P = 0.017), while diffuse proliferative changes were more common in group B (P = 0.031). The course of the IgAN was thus often very protracted, with some children developing hypertension as well as decreased renal function. However, after a period of 8 years or more of follow-up half of the patients did not show any clinical signs of the disease, which may indicate low disease activity or, possibly, recovery.