The premature has a reduced number of nephrons. This condition, added to an immature renal function at birth, increases the vulnerability to hemodynamic changes, drug toxicity, and nephrocalcinosis. The oligonephronia worsens the risk to present in adulthood, hypertension and renal insufficiency. Nephrocalcinosis appears in the postnatal period, secondary to renal calcifications. This condition increases the risk of further renal endowment. The nephrocalcinosis is closely related to rickets in the premature. Indeed, an excess of vitamin D and calcium, increases the risk of nephrocalcinosis. The early recognition of markers, such as microalbuminuria, hypertension and hypercalciuria, allow targeting prevention measures.