Objectives: Ultrasound-guided percutaneous nephrolithotomy (PCNL) has become increasingly utilized. Patients with nondilated collecting systems represent a challenge: the target calix is often difficult to visualize. Here we report pilot study results for retrograde ultrasound contrast injection to aid in percutaneous renal access during ultrasound-guided PCNL. Patients and Methods: From April to July 2016, consecutive patients over the age of 18 years with nondilated collecting systems on preoperative imaging who presented for PCNL were enrolled. B-mode ultrasound imaging was compared with contrast-enhanced mode with simultaneous retrograde injection of OptisonÔ via an ipsilateral ureteral catheter. Results: Five patients (four males and one female) with renal stones underwent PCNL with retrograde ultrasound contrast injection during the study period. Mean body mass index was 28.3 -5.6 kg/m 2 and mean stone size was 24.5 -12.0 mm. Under B-mode ultrasound, all patients demonstrated nondilated renal collecting systems that appeared as hyperechoic areas, where it was difficult to identify a target calix for puncture. Retrograde contrast injection facilitated delineation of all renal calices initially difficult to visualize under Bmode ultrasound. Renal puncture was then performed effectively in all cases with a mean puncture time of 55.4 -44.8 seconds. All PCNL procedures were completed without intraoperative complications and no adverse events related to ultrasound contrast injection occurred. Conclusion: Retrograde ultrasound contrast injection as an aide for renal puncture during PCNL is a feasible technique. By improving visualization of the collecting system, it facilitates needle placement in challenging patients without hydronephrosis. Future larger scale studies comparing its use to standard ultrasound-guided technique will be required to validate this concept.