Data on 469 patients (251 boys, 218 girls) aged 0-22 years treated with renal replacement therapy (RRT) at 13 pediatric dialysis units in Poland from 2000 to 2004 were analyzed. Congenital and genetic renal diseases were the cause of ESRF in 56% of the polish population of children and adolescents on RRT. 39% of causes were acquired diseases, 5% remained unidentified. Congenital and genetic causes dominated in children < 5 years of age (71%). They accounted for 49%, 61% and 45% of causes in the consecutive 5-year age groups.