© 2016 American Urological Association Education and Research, Inc. Purpose The increasing incidence of pediatric nephrolithiasis is a growing concern and its association with obesity continues to be an area of debate. We present data on urine chemistries of overweight/obese children compared to those with a normal body mass index and history of urolithiasis treated at a single institution in the United States, and assess risk factors. Materials and Methods We retrospectively identified 110 stone forming patients who underwent 24-hour urine collection and stratified them according to the Centers for Disease Control and Prevention definitions of overweight/obese (body mass index above 85th/95th percentile). Absolute urine collection quantities were compared between groups. Stone risk factors were analyzed according to Litholink® specified reference ranges. Results Compared to patients with low or normal body mass index, overweight and obese patients had lower body surface area adjusted citrate (242 mg/1.73 m2 vs 315 mg/1.73 m2, p = 0.03), lower urine phosphate (12 mg/kg vs 14 mg/kg, p = 0.04), lower urine magnesium (1.2 mg/kg vs 1.6 mg/kg, p = 0.01) and increased incidence of hypercalciuria (31% vs 11%, p = 0.02). Differences in urine citrate, phosphate and magnesium were not apparent when analyzing stone risk factors. There was no association between body mass index and urine pH. Conclusions Overweight and obese stone forming children have decreased levels of urine citrate, phosphate and magnesium compared to patients with normal body mass index. The incidence of hypercalciuria is increased in overweight/obese patients. In contrast to findings in adults, there is no association between urine pH and body mass index.