The diagnosis of granulocytic sarcoma has frequently been a problem for the pathologist because of the immature nature of the tumor. One other group of difficult-to-diagnose tumors is the small round cell tumors of childhood, which lack any particular morphologic feature that would allow a precise diagnosis. This report describes a 9-month-old boy with a soft tissue mass on the left ankle initially diagnosed as small round cell malignant tumor, who 2 months from diagnosis developed another tumor simultaneously with the blood and bone marrow manifestations of acute nonlymphocytic leukemia. Following leukemic manifestation, the retrospective diagnosis of granulocytic sarcoma was made. It is suggested that granulocytic sarcoma should be included in the differential diagnosis of small round cell tumors in children.