Objectives: the aim of this study was to determine the dyamics of occurence of microdeletion/microduplication syndrome, characteristics of the genealogical tree, perinatal risk factors, clinical, phenotypical and genetic characteristics. Study design: the study was conducted as a cross - sectional study. Subjects and methods: subjects are children who were diagnosed with microdeletion or microduplication syndrome (MMS) in KBC Osijek from 2011. to 2021. Data was collected from medical records and the hospital information system for 31 patients. The following was acquired: data on the mother, pregnancy and clinical characteristics of children. Results: the arithmetic mean age of the children at the time of the research was 6,9 years, and there were equal numbers of both sexes. The age of the father at the time of conception was significantly higher than the age of the mother, but it is not considered a risk factor for the occurance of MMS as well as chronic diseases of the mother and the father. A quarter of children had intracranial bleeding or asphyxia, and every third child required treatment immediately after birth. The majority of children were born at term with an average gestational age of 39 weeks, a normal birth weight of 3090 g on average and a normal APGAR index. A previous spontaneous abortion was found in 19.4 % of pregnant women. The results of the analysis of the observed phenotypic features showed that almost 50 % of children with MMS have early - present elements of facial dysmorphia. Clinically, CHD is present as the most common anomaly, as well as slow psychomotor and speech development along with some form of intellectual retardation. Conclusion: Microdeletion and microduplication syndromes appear in children independently of maternal and perinatal risk factors, but depend on an error occurring during cell division. In two - thirds of patients, the genetic basis of the phenotype is known, and in one - third, the influence of affected genes on the clinical picture is not clear.