The authors present results of systematic use of percutaneous renal biopsy in children in the first three years of practice. From 1986 to 1989, 153 renal biopsies were done in 144 children and adolescents (75 males, 69 females) aged 4 months to 18 years. The most common indications were as follow: primary nephrotic syndrome, most often resistant to corticosteroid treatment (28.5%), haematuria (28.5%), secondary glomerulopathies, either with or without nephrotic syndrome (9.7% and 15.3%, respectively), and proteinuria (4.9%). 90.8% of biopsies were successful obtaining adequate tissue for light microscopic diagnosis, containing a n average number of 16 glomeruli. An overall number of 29 complications (18.9% of biopsies) in 23 patients was observed. Gross haematuria was the most common, lasting no more then one (9.8% of biopsies) or three days (2.6%) requiring blood transfusions in three cases (1.96% of biopsies). Others complications were fever (1.96%), perirenal haematoma (1.3%), and severe pain at the site of biopsy (1.3%). There were no significant differences between three annual periods with regard to the incidence of successful biopsies or complications, but more serious complications occurred during the first year of practice. In children younger than five years the rate of successful biopsies was higher and incidence of complications was lower than in older children. The authors' results correlate favourably with data published in the foreign literature.