Segmental renal hypoplasia or Ask-Upmark kidney is an extremely rare anomaly that induces severe arterial hypertension in young patients. Two new cases of this entity are presented respectively in a 39 and 31 years old women who are admitted for hematuria, elevated blood pressure level and flank pain. Surgical treatment of the hypoplasia kidney permitted successful treatment of the high blood pressure with preservation of renal function and flank pain. In view of the literature, the authors discuss the pathogenic, diagnostic and therapeutic aspects of this condition.