More than 325 000 Americans are hospitalized each year for the evaluation and treatment of calculi in the urinary tract. It is estimated that an equal number of unfortunate victims of urolithiasis are treated exclusively as outpatients. For years, the problem of urolithiasis was considered to be the scourge of the adult years. Recently, an increasing awareness of the importance of urolithiasis in children has developed. Clearly, urinary stones—or warning signs of future calculi—occur in children, especially in certain geographic regions and in high-risk populations. Recognition of children at greatest risk may allow early detection or prevention of calculus formation based on a laboratory evaluation directed at pathogenetic risk factors known to be important in the formation of nephrolithiasis. CLINICAL MANIFESTATIONS OF UROLITHIASIS The classical image of incapacitating flank pain associated with the passage of a urinary calculus is unusual in children. Abdominal or flank pain occurs in approximately 50% of children with urolithiasis; in infants, symptoms of stones may be confused with colic. In older children, abdominal pain may be vague and nonspecific, as well as severe and radiating into the groin. Hematuria, either microscopic or macroscopic, occurs in greater than 90% of children with urolithiasis. Urolithiasis should always be a consideration in children with nonglomerular hematuria especially in geographic regions where nephrolithiasis is common.