We evaluated a subset of infants with bilateral markedly hyperechoic "bright" kidneys noted prenatally in association with normal amniotic fluid volume during gestation. Prenatal ultrasound showed increased renal parenchymal echogenicity bilaterally with preservation of the medullary pyramid architecture. These children were followed for up to 3 years to determine potential changes in the sonographic appearance of the echogenic renal parenchyma and to assess renal function. In 3 years 8 cases of bilateral hyperechoic fetal kidneys were identified. During postnatal followup renal echogenicity resolved in 4 cases, diminished in 1 and remained the same in 3. The serum creatinine and electrolytes were normal in all cases followed for more than 3 months. Other renal findings included vesicoureteral reflux in 2 of 7 cases, mild pelvic ectasia in 1 and tiny medullary calcifications in 1. The specific etiology of increased echogenicity is unknown, although 1 infant appeared to have a form of autosomal recessive disease with liver hyperechogenicity as well. We conclude that fetuses with bilateral hyperechoic kidneys associated with normal amniotic fluid volume have a favorable outcome. Ultrasonographic finding of marked parenchymal hyperechogenicity appears to improve with time; in our experience renal function is normal and the infants thrive. Continued followup is necessary to determine the long-term natural history of this phenomenon, as is subsequent prenatal and postnatal evaluation of future siblings to assess genetic risk.