TITLE: Clinical and cytogenetic features of leukemias in children treated in the Pediatric Department of KBC Osijek OBJECTIVES: The aim of this study is to examine the clinical characteristics, frequency and outcome of lymphoproliferative diseases and their difference in relation to age, sex, comorbidities, perinatal risk factors and family history; determine the types of chromosomal abnormalities and immunophenotype. STUDY DESIGN: A cross-sectional study with historical data. PARTICIPANTS AND METHODS: The research was conducted at the Pediatric Clinic of Clinical Hospital Center Osijek in the period from 2017 to 2023. By reviewing the medical documentation, demographic, clinical, biochemical, hematological, and genetic data were collected in 30 subjects with diagnosed leukemia and lymphoma. RESULTS: In the observed period, 30 children with lymphoproliferative diseases (LPD) were diagnosed, with an incidence of 5 children per year, and a higher incidence of leukemia (63 %) versus lymphoma (37 %). The median age at diagnosis of leukemia is 5 years, and 13 years for lymphoma. The occurrence of LPD is higher in male pediatric population (63 %). There are no differences in the occurrence of LPD considering a positive family history, comorbidities, and perinatal factors. Supraclavicular and cervical lymphadenopathy (63 %), fever (57 %) and pallor (53 %) are the most common clinical features in children with LPD. Immunophenotyping revealed blasts of the lymphoid lineage in 86 % of subjects, while cytogenetics confirmed the presence of structural and numerical chromosomal aberrations in 60 %. After establishing the diagnosis by cytogenetics and immunophenotyping, treatment is started according to the protocols by which all children achieved complete remission. CONCLUSION: There is no difference in the occurrence of LPD in relation to gender, comorbidities, perinatal risk factors and family history, but the difference exist in relation to age. Determining the presence of chromosomal aberrations leads to adequate treatment with a favorable outcome among patients.