急性淋巴性白血病（英语：Acute lymphoblastic leukemia，ALL），是因为体内淋巴细胞不正常增生造成的血液疾病。淋巴是人体免疫系统的重要环节，由骨髓与淋巴结所制造。而急性淋巴性白血病的成因即为淋巴母细胞因不明原因的成熟障碍，导致过度增生，进而压制正常骨髓造血组织，并造成周边血管、骨髓、全身淋巴结、脾脏与肝脏的浸润。临床上，急性淋巴性白血病的症状包括因白血球减少而引起感染、发热，通常还会伴有淋巴结与肝脏、脾脏的肿大，这些症状在儿童身上最为明显。此外急性淋巴球白血病容易侵犯人体的中枢神经系统，检查时需做脑脊髓液检测。

Acute lymphoblastic leukemia, also known as acute lymphocytic leukemia or acute lymphoid leukemia (ALL), is an acute form of leukemia, or cancer of the white blood cells, characterized by the overproduction and accumulation of cancerous, immature white blood cells, known as lymphoblasts. In persons with ALL, lymphoblasts are overproduced in the bone marrow and continuously multiply, causing damage and death by inhibiting the production of normal cells (such as red and white blood cells and platelets) in the bone marrow and by spreading (infiltrating) to other organs. ALL is most common in childhood, with a peak incidence at 2–5 years of age and another peak in old age.