The natural history of autosomal dominant polycystic kidney disease (ADPKD) has not been well described in children, and it is not known whether a relationship exists between renal structural abnormalities and function in children as has been seen in adults. Therefore, 140 children from 67 ADPKD families were studied in a prospective study. Only 22 children came with a previous diagnosis of ADPKD. In 44% of all children, at least one cyst was found on ultrasound at a mean age of 8.7 yr. Of these, 60% were classified as having moderate disease on the basis of a total cyst number of 1 to 10 cysts, whereas 40% were considered to have severe disease with a total of more than 10 cysts. There was a significant relationship between the severity of the renal structural involvement and the frequency of flank and back pain, hypertension, and impaired renal concentrating capacity. However, GFR were not reduced in children with ADPKD and did not relate to structural severity. Thirty-nine children were seen for a follow-up visit 2 to 5 yr after the initial visit. No child had progressed from nonaffected to affected with ADPKD, but three of four children with only one cyst at the time of the initial study had progressed to bilateral cysts. Among the 22 ADPKD children who had a follow-up study, there was progression of the disease, reflected by an increase in cyst number and an increase in the frequency of pain and hypertension. However, GFR remained stable in all children.(ABSTRACT TRUNCATED AT 250 WORDS)