Nephromegaly in infancy may be due to several causes, being the most relevant: renal polycystic autosomic recessive disease, venous renal thrombosis, deposit diseases, kidney tumors, nephrotic congenital syndrome and neoplastic infiltration. Although renal infiltration is relatively frequent in acute lymphoblastic leukemia, nephromegaly is an unusual form of presentation in this pathology. The case of a four-year-old patient, who presents bilateral nephromegaly and pancytopenia, is presented. Acute Lymphoblastic Leukemia is diagnosed, initiating the corresponding chemotherapic treatment.