Background: Acute Lymphoblastic Leukemia (ALL) is a type of cancer of blood and bone marrow. It is a fast-growing cancer that predominantly affects the lymphoid lineage of white blood cells, leading to the overproduction of abnormal lymphoblasts. It is the most frequently diagnosed form of leukemia in children, though it can also occur in adults. Objective: This study aimed to determine the association between TYMS (rs 2853542) gene polymorphism and the percentage of CMV in patients with ALL. Patients and methods: A case-control study was carried out on one hundred twenty blood specimens, including sixty patients referred to the national center of hematology/al Mustansiriyah University and diagnosed with Acute lymphoid leukemia and sixty specimens collected from persons as a healthy control group, from October 2023 to June 2024. Sequencing was used to identify TYMS (rs 2853542) gene polymorphism and the genome of Cytomegalovirus by using conventional PCR. Results: Out of 120 individuals, 60 patients diagnosed as ALL with a mean age (15.9±11.4) years and 60 healthy control group with a mean age (17.8±12.3) year. The difference in the frequency of the TYMS (rs 2853542) genotype distribution between patients and control groups was statistically significant. PCR testing for CMV revealed positive results in 8.3% (5 out of 60 cases) of ALL patients. While 3.3% (2 out of 60 cases) have positive DNA-CMV genome in AHC group, so there is non-significant value between these groups, High significance value was found between TYMS (rs 2853542) SNP and CMV- DNA in patients with ALL.