Renal agenesis is the absence of any trace of kidney, ureter, and therefore the absence of fetal renal function. It constitutes a major field of antenatal screening which presents until now certain limits during ultrasound diagnosis which remains the only accessible, inexpensive and reproducible means of exploration for making the diagnosis with a sensitivity of 85%. The neonatal prognosis is considered better in the unilateral Renal agenesis with functional contralateral kidney, but is always fatal in its bilateral form. The objective of our study is to clarify the ultrasound strategy that must be adopted in antenatal to make the diagnosis while highlighting the technical difficulties that can misdiagnose. An update on the epidemiological and etiopathogenetic nature of the anomaly will also be discussed.