Optical Genome Mapping for diagnosis of paediatric leukaemia Cytogenetics has led to the discovery of multiple chromosomal anomalies associated with hemato-oncologic diseases in children and adolescents. The Hospital Infantil Universitario Niño Jesús is a Spanish reference center for pediatric leukemia. To date, the clinical cytogenetic analyses are a combination of karyotyping (KT), fluorescence in situ hybridization (FISH) and PCR to detect genetic biomarkers of the disease. We show that optical genome mapping (OGM) arises as a new technology of one step with a higher resolution than karyotype, FISH and CNV-microarrays able to detect structural variants and copy number variation clinically relevant for pediatric leukemia. We analyzed 26 samples from patients with acute lymphoblastic leukemia and 7 samples from patients with acute myeloid leukemia by OGM and the results were compared with the results obtained with the traditional diagnosis techniques. We obtained 100% of concordance between conventional and OGM technologies for both types of leukaemia, and not only that, but also, we demonstrated that OGM refined the structural variant found and defined new abnormalities. All together, these data demonstrate the improvement of leukaemia diagnosis by OGM as an alternative for clinical cytogenetic.