Infant leukemia is a very rare disease and consists of 5% of all childhood leukemias. Infant leukemia usually presents with high leukocyte counts and numerous extra-hematological features including central nervous system and skin involvement. Herein, we report a 1-month-old girl presented with high phenylalanine level in national newborn screening program for phenylketonuria; and subsequently diagnosed to have acute lymphoblastic leukemia.