The goal of this observational study is to learn about the benefit of using RetroPerc® in obtaining renal access for percutaneous nephrolithotomy. The device is already used in routine clinical practice by urologists around the country.

Participants who are already scheduled to undergo percutaneous nephrolithotomy as part of their regular care will be asked to participate.

Retrograde nephrostomy access is well established as a safe method for nephrostomy creation and thus this study aims to perform a standard of care study. The device is already available, on the shelf, and used in routine clinical care. However, the study aims to take a closer look in a prospective fashion at this access technique to better understand specific variables that are not available on retrospective review of cases that have already undergone PCNL with this technique.

Inclusion Criteria:

• Renal stone or total linear sum of 1.5-3cm cm in maximum dimension (largest diameter in axial or coronal)--- multiple stones should be summed to determine stone size.
• Age >=18 years of age
• Gender: both men and women included.
• Ethnic background: all ethnicities will be included in the study population and the specific ethnic diversity present in the study population will reflect the geographic distributions of the participating institutions.
• Plan for PCNL in the supine position

Exclusion Criteria:

• Active pregnancy
• BMI >45
• Severe Hydronephrosis - renal pelvis diameter > 20mm
• Flank window < 4 cm are ineligible for puncture
• Previous ipsilateral PCNL
• Currently with "useful" nephrostomy tube on ipsilateral side
• Uncorrectable coagulopathies
• Untreated urinary tract infection
• Subjects with significant morbidities such as American Society of Anesthesiologists (ASA) score ≥ 4, severe spinal cord injuries, severe cardiopulmonary insufficiency, uncontrolled diabetes, neurological disorders, bedbound, anticipated life expectancy less than 5 years, or any other comorbidity, that in the opinion of the principal investigator could represent an increased peri-operative risk for the subject;
• Ipsilateral partial nephrectomy
• History of ipsilateral ureteral reimplantation or ureteral reconstruction;
• History of Simple or radical prostatectomy
• History of cystectomy
• History of calyceal diverticula stone;
• History of renal donation or transplant;
• Any other previous pelvic surgical treatment that could put the subject at greater procedural complication risk or technical difficulty;
• Ureteral ipsilateral stricture, untreated;
• Ureteral stricture, untreated (not to include "tight" ureter);
• Any other bladder, ureteral or kidney congenital genitourinary abnormalities (e.g. Horseshoe kidney, ipsilateral duplicated or partially duplicated collecting system, ipsilateral ectopic kidney, cross-fused ectopia, bifid renal pelvis with no horizontally directed calyces, solitary kidney, etc.) preventing the ability to direct a puncture laterally or render the subject stone free;
• Have participated in any other clinical trial within the last 3 months, and/or plans to participate in any other investigational or invasive clinical trial during this study;
• If female, breast-feeding, or if childbearing age, is not using contraception between screening and 90 days post-op;
• Subject has current or recent history of substance abuse (e.g. recreational drugs, narcotics, or alcohol) requiring intervention;
• Is a prisoner or ward of the state;
• Is unable to meet the treatment and follow up protocol requirements.

Participants undergoing percutaneous nephrolithotomy for treatment of their renal stone (s) total linear sum of 1.5 to 3cm cm in maximum dimension.

De-identified participant data collected during the study

Following end of study

Data may be requested by participating study investigators. The participating sites must have a data use agreement in place before requesting access to the data.