Purpose: The purpose of this study was to assess the efficacy of a modified percutaneous nephrostomy procedure for grade III-IV hydronephrosis in neonates. Material and methods: Eleven neonates (five girls, six boys) with a mean age of 13.7days±9.9 (SD) (range, 4-28days) with pronounced hydronephrosis had percutaneous nephrostomy using a modified procedure. In all patients, percutaneous nephrostomy was performed with a trocar catheter under ultrasound guidance and then the catheter was placed into the collecting system without prior dilatation. Results: Technical success was achieved in all patients. There were no major procedure-related complications. There was no perirenal hematoma on control ultrasound examinations and no hematuria was observed after the procedure. The median drainage time was 75days (range: 42-120days). Two children had urinary tract infection, which was controlled by using antibiotics. Conclusion: The trocar nephrostomy is a practical and feasible method, which can be used for neonates with grade III-IV hydronephrosis.