A 7-year-old boy was referred with a provisional diagnosis of bilateral Wilms tumor. Peripheral smear revealed elevated leukocyte count with 90% blasts. Bone marrow aspiration and biopsy were hypercellular with sheets of blasts. Immunohistochemistry on paraffin sections showed a pre-B phenotype of acute lymphoblastic leukemia. Computerized tomographic scan of the abdomen showed moderate bilateral renal enlargement. Ultrasound-guided fine needle aspiration cytology of both kidneys showed blasts similar to those seen in the bone marrow. Finally, a diagnosis of pre-B acute lymphoblastic leukemia infiltrating both the kidneys was made. This case is being presented because of its rarity.