INTRODUCTION: Infantile leukemia encompasses a heterogeneous group which needs stratifying for treatment selection. METHODS: We collected 78 cases of infantile leukemia and retrospectively analyzed their clinicopathological data. RESULTS: Infantile leukemia featured a ratio of acute myeloid leukemia (AML) to B-lymphoblastic leukemia (B-ALL) of 1:2, with a better survival for AML than B-ALL (median survival 36 vs 24 months). When stratified by age, "early" infantile B-ALL (2-6 months) showed a high rate of KMT2A rearrangement (100%), similar to the rate seen in congenital B-ALL (1 month) (100%) and higher than seen in "late" infantile B-ALL (≥7 months) (68%). The three categories of infantile B-ALL exhibited an age-dependent increase in survival (median survival 8.5, 24, and >24 months, respectively). The age-dependent survival benefit remained after excluding the cases negative for KMT2A rearrangement. Conversely, infantile AML lacked an age-dependent pattern of survival. CONCLUSION: The clinical outcome of infantile leukemia depends on the type of leukemia. Given the age-dependent survival, infantile B-ALL can be divided into three subcategories.