Medullary sponge kidney is reported in six children aged 2-18 years. One child was asymptomatic; the others had hematuria or a urine-concentrating defect. Renal function and size were otherwise normal, as was liver function. The diagnosis was made at excretory urography according to criteria established in adults. Sonography revealed hyperechogenic pyramids, at first at the periphery, later generalized. Computed tomography proved this to be calcium. Medullary sponge kidney is rare but exists in children. Sonography is very sensitive to the pyramidal nephrocalcinosis that complicates this disease and explains the frequent presenting symptom of hematuria in these children.