© Mary Ann Liebert, Inc. 2016. Introduction: No method currently exists for predicting which young child with a renal or ureteral stone will require surgery as opposed to pass the stone. Our goals were to analyze practice patterns at a major pediatric center and to identify factors that predicted spontaneous stone passage. Method: A retrospective review of all prepubertal patients (≤ 11 years) presenting to our institution from January 2005 to July 2014 with symptomatic nephrolithiasis was performed. Demographic data and stone details were reviewed, including anatomic location, size, and outcomes. Spontaneous stone passage was determined by parental report and/or stone absence on imaging obtained within 6 months after initial diagnosis. Results: A total of 119 eligible patients were identified, with an average age of 88.7 months (4-143). Forty eight (40.3%) patients spontaneously passed their stone and the remaining 59.7% required endoscopic intervention. Overall, 79.0% had symptomatic presentation (flank pain, hematuria) and 39.5% of patients were obstructing stones. Symptomatic presentation was more common with ureteral (86.5%) than with renal (66.7%) stones, but was not associated with increased passage of stones in general (p-value 0.1765). Of the 48 patients who spontaneously passed stones, 11 (24.4%) were renal stones compared with 37 (50.0%) ureteral stones. The average size of spontaneously passed stones was 3.5 mm (2-8) for renal and 3.4 mm (1-7) for ureteral stones. Based on logistic regression, the single most important predictor of stone passage was stone size (p-value <0.001). The odds of passage were 3.1 times higher for ureteral stones compared with renal stones (p = 0.0070) when not controlling for size. Conclusion: In prepubertal patients, ureteral stones with an average size of 3.5 mm or less are more likely to pass spontaneously. Based on this information, watchful waiting is a reasonable option in clinically stable nonseptic patients with renal/ureteral stones of this size.