The renal venous thrombosis is mostly produced by severe dehydration. The following, however, are also predisposing factors: infections, birth traumata, paranephritic processes, lack of oxygen, diabetes of the mother and cyanotic heart defects. The diagnosis is correctly made by means of the palpable flank tumor, the macrohematuria, together with the urogram and sonography. The most urgent therapeutic measure is the balancing of the water and electrolyte deficit to eliminate the dehydration, i.e. the existing oliguria or anuria. The therapy is primarily always conservative. In the event of a consumption coagulopathy, a therapeutical attempt can be undertaken with heparin but if this is unsuccessful, an immediate nephrectomy must be performed. A further nephrectomy will be necessary if hypertony persistent infection and renal atrophy occur. Two infants with renal venous thrombosis were used for this study on the causes and diagnosis of, and the therapy for the illness.