Urolithiasis in pediatric patients has been perceived as uncommon, and the appropriate evaluation and management have been controversial. To determine the clinical characteristics, types of stone problems, and outcomes of pediatric patients with urolithiasis encountered in a referral center, we retrospectively assessed 221 patients (113 girls and 108 boys) with urolithiasis examined at the Mayo Clinic between 1965 and 1987. The median age at onset of symptoms was 11 6/12 years among the female patients and 10 6/12 years among the male patients. Analysis of stone constituents in 122 patients showed the proportion of calcium oxalate (44.7%), calcium phosphate (23.6%), and cystine (8.1%) stones to be similar in all age-groups. Overall, struvite stones were found in 17.1% and uric acid stones in 1.6% of patients. Conditions that predisposed to metabolic urolithiasis were identified in 115 patients (52%). Hypercalciuria was confirmed in 49 of 145 patients (33.8%) and hyperoxaluria in 25 of 124 (20.2%). Eight of 96 patients had hyperuricosuria, and 5 of 54 had hypocitraturia. Forty-one patients (18.6%) had infection-related stones. Of 66 patients with structural anomalies of the genitourinary tract, 24 (36%) had metabolic abnormalities and 26 (39%) had chronic infection. Among patients with chronic infection, 29% had metabolic abnormalities. Of the 221 patients, 148 (67%) had two or more stones during a mean follow-up of 59 months. Among 140 patients with 12 months or more of follow-up, metabolic activity was present in 31 (22.1%) at the time of most recent examination. Overall, 166 of 221 children (75.1%) were found to have factors that predisposed to urolithiasis.(ABSTRACT TRUNCATED AT 250 WORDS)