Aim of work: to evaluate the efficacy and safety of US guided PCNL for isolated renal pelvis stone > 20mm in maximum diameter.Methods: a prospective interventional study which conducted on a group of 24 patients with renal stones treated by US guided PCNL at Zagazig university hospital, department of urology. all cases that fit the inclusion criteria were enrolled in our study with informed consent.Results: shows that the age of the study group was (35.8±8.5) ranged from (23 to 51) years, their BMI was (23.5±3.8) ranged from (18 to 30) kg/m2 and (79.2%) of them were males. Also shows that (70.8%) of the study group didn't have any chronic diseases, (12.5%) of them were hypertensive and (12.5%) were hypertensive& diabetic. Also shows that the stone size of the study group ranged from (22 to 35) mm, stone density ranged from (385 to 1570) HU, (58.3%) had left renal pelvis stone and (87.5%) of them were radio-opaque. Success rate of procedure under U.S guidance was (87.5%) (success cases) of the remaining (12.5%) we failed to get an access under US guidance so we needed to conversion to conventional fluoroscopic guidance (failed cases) after 3 trials under US guidance. Conclusion: Percutaneous nephrolithotomy with ultrasound guidance is a good alternative to the fluoroscopic method , can be performed safely without radiation exposure to the patients and medical staff , with satisfactory outcomes without any major complications , in patients with single renal pelvis stone with mild to moderate hydronephrosis.