OBJECTIVE. The aim of our study was to examine long-term effects of nephrocalcinosis in prematurely born children. PATIENTS AND METHODS. Preterm neonates (gestational age < 32 weeks) with (n=42) and without (n=32) nephrocalcinosis were prospectively studied at a mean age of 7.5 (+/- 1.0) years. RESULTS. Blood pressure did not differ in ex- preterm infants with and without nephrocalcinosis but was significantly higher than expected for healthy children. In comparison to healthy children, more ex- preterm infants with neonatal nephrocalcinosis had (mild) chronic renal insufficiency (glomerular filtration rate: < 85 mL/ min per 1.73 m(2); 6 of 40); this is in contrast to ex- preterm infants without neonatal nephrocalcinosis (2 of 32). Tubular phosphate reabsorption and plasma bicarbonate were significantly lower in children with nephrocalcinosis compared with children without nephrocalcinosis. In addition, more ex- preterm infants with and without nephrocalcinosis than expected had low values for plasma bicarbonate and early- morning urine osmolality compared with healthy children. Kidney length of ex- preterm infants with and without nephrocalcinosis was significantly smaller than expected in healthy children of the same height. Nephrocalcinosis persisted long- term in 4 of 42 children but was not related to blood pressure, kidney length, or renal function. CONCLUSIONS. Nephrocalcinosis in preterm neonates can have long- term sequelae for glomerular and tubular function. Furthermore, prematurity per se is associated with high blood pressure, relatively small kidneys, and (distal) tubular dysfunction. Long-term follow-up of blood pressure and renal glomerular and tubular function of preterm neonates, especially with neonatal nephrocalcinosis, seems warranted.