Although pediatricians are frequently confronted with patients presenting urolithiasis symptoms without obvious stones, the syndrome of occult urolithiasis may be still viewed with some skepticism. We have compared the clinical and metabolic features of 197 children with obvious calculi, 189 with microcalculi (diameter ≤ 3 mm based on renal sonography), and 114 with symptoms of urolithiasis and normal renal sonography findings. Only microcalculi and normal sonography subjects with a urinary abnormality potentially leading to urolithiasis were included in the study. Age at presentation increased significantly (p = 0.0001) in the groups in the order normal sonography to microcalculi to calculi groups. There was no significant difference among the three groups in terms of family history of urolithiasis, gender distribution, and degree of hypercalciuria, hyperuricosuria, hyperoxaluria, or hypocitraturia. The average frequency of pain attacks of patients with recurrent abdominal pain (RAP) ranged from 3.6 to 4.6 days of pain per month among the three groups, which is four to ninefold lower than that reported for children with functional or organic gastrointestinal RAP. The consistency of many clinical and urinary metabolic characteristics indicates a common underlying disorder in overt and occult urolithiasis. The increase of age at presentation from the normal sonography to microcalculi and calculi groups may reflect progressive crystal accretion leading ultimately to overt stone formation.