Acute leukemia is a type of bone marrow cancer in which a group of cells in the bone marrow that produce white blood cells, called leukocytes, become abnormal and multiply rapidly in a short period. This proliferation reduces blood production in the bone marrow. The word "acute" signifies that these leukemia types can progress rapidly if left untreated and may be fatal within months.

There are two types:

Acute myeloid leukemia (AML)
Acute lymphoblastic leukemia (ALL)

AML is also known by many other names, including acute myelocytic leukemia, acute myelogenous leukemia, acute granulocytic leukemia, and acute non-lymphocytic leukemia. "Myeloid" refers to the type of cell in the bone marrow where this leukemia originates. Most cases of AML develop from cells that would become white blood cells (other than lymphocytes), but some AML cases can develop from other blood-forming cells.