• Hypercalciuria (HCU) is frequently found during the evaluation of children with hematuria; the long-term implications of untreated HCU in children are uncertain. Since 1981, we have identified HCU (urinary calcium, >0.1 mmol ·kg−1·d−1) in 58 patients (41 male) with hematuria; 64% had gross hematuria and 74% had a relative with urolithiasis. Renal HCU was diagnosed in 19 patients and absorptive HCU in 24 patients. In 15 children, the calcium loading test was nondiagnostic. In nine patients (16%), urolithiasis developed, and in one patient, a renal calcification developed. These 10 patients (seven male) were older (10.1 vs 7.5 years) than the other 48 patients and initially presented with gross hematuria (nine of 10). All 10 patients had a family history of urolithiasis. The initial urinary calcium value was similar between the 10 patients with stones (0.15 mmol·kg−1·d−1) and the patients without stones (0.14 mmol·kg−1·d−1); five had absorptive HCU and four had renal HCU. At least one follow-up urinary calcium measurement was available for 23 patients who were not receiving thiazide therapy during 1 to 6 years after diagnosis (mean, 3.1 years). At 1-year follow-up, 12 of 17 patients had HCU and five had hematuria. Twenty-one patients were studied 2 to 3 years from diagnosis; 11 had HCU and eight had hematuria. After 4 years, six of seven patients had HCU and three had hematuria. We conclude that children with HCU and hematuria are at significant risk for urolithiasis, especially if they have gross hematuria and a family history of urolithiasis. Hypercalciuria may be episodic in children with hematuria, and factors other than urinary calcium concentration may be responsible for urinary bleeding.