Denys-Drash syndrome is a rare symptom complex associated with obligatory childhood nephrotic syndrome, male pseudohermaphroditism, and Wilms' tumor. The etiology of Denys-Drash syndrome is attributed to a mutation of the WT1 gene. We report on two cases of Deny-Drash syndrome confirmed by genetic testing. Rapidly evolving terminal renal insufficiency was detected in both patients necessitating bilateral nephrectomies with prophylactic intent. In one of the patients, a Wilms' tumor had already been verified in one kidney so that chemotherapy had to be initiated.The risk of Wilms' tumor is very high in patients with a WT1 mutation, which leads to the need for removal of both kidneys during or before transplantation. It would be important to perform a diagnostic work-up for WT1 gene mutation in children who develop renal failure in the 1st year of life.