A retrospective study of 68 children with increased medullary echogenicity on renal ultrasound (US) examination showed nephrocalcinosis to be present in 42 patients. The cause was believed to be iatrogenic in 30 and noniatrogenic in 12. Furosemide therapy was responsible for 11 of the cases of iatrogenic nephrocalcinosis and vitamin D therapy for the remaining iatrogenic cases. Noniatrogenic nephrocalcinosis was seen with hypercalcemia, hypercalciuria, renal tubular acidosis and dystrophic calcification following renal tubular necrosis. In 26 patients, medullary deposits of urates or proteins, medullary fibrosis, or vascular congestion (due to a variety of diseases) appeared to account for the finding. These possibilities should be added to the differential diagnosis of hyperechoic renal pyramids when nephrocalcinosis is unlikely.