Acute lymphocytic leukemia (ALL) is a cancer of the white blood cells characterized by excess lymphoblasts. It is most common in children aged 2-5 years old and causes damage by crowding out normal bone marrow cells. ALL is diagnosed through blood tests, bone marrow biopsies, and other exams. Risk factors include radiation, chemicals, viruses, and genetic syndromes. In the United States, about 4,000 people are diagnosed with ALL each year, with higher rates for whites and males. The 5-year survival rate is approximately 65% for Caucasians.