Urolithiasis is increasingly recognized in pediatric patients and is encountered in a variety of clinical settings: the 8-year-old boy who presents with hematuria, the 14-year old with cystinuria experiencing her fourth episode of renal colic in the past 6 years, the 10-year old with inflammatory bowel disease whose two renal stones were recognized incidentally during imaging for evaluation of abdominal pain, the premature infant with asymptomatic nephrocalcinosis and a stone, the 4-year old in the emergency room with gross hematuria and abdominal pain after recently starting indinavir medication. All have in common particulate material of mineral origin within the urinary tract. An understanding of how and why stones form, along with knowledge of the pathophysiologic states that promote urinary tract calculi, provide the basis for effective clinical management.