In children older than 2 years, hypercalciuria is the most common metabolic cause of renal stones. In infants, its prevalence is not well established. Since 1990, we observed five infants in whom renal stones or microcalculi were diagnosed between the age of 5 and 19 months. One of them was lost to follow up. In the present report, we describe the four patients who underwent metabolic evaluation and in whom idiopathic hypercalciuria (IH) was diagnosed. We conclude that IH is a frequent cause of microcalculi and renal stones in infants, and a screen for this condition is warranted in this age group.