Chromosomal abnormalities are the leading cause of intellectual disability. They are associated with congenital anomalies that may result in perinatal death or with the birth of a child with malformation. The aim of this study was to present the frequency of numerical and structural chromosomal aberrations and to list the indications for prenatal diagnosis in the cytogenetic laboratory at the Department of Medical Biology and Genetics, Faculty of Medicine, University of Rijeka, in the period from 1stJanuary 2004 until 1stSeptember 2020. In the observed period, 4054 samples of amniotic fluid were analyzed. Normal karyotype was detected in 3837 (94.6%) samples, while the remaining 217 (5.4%) samples showed an aberrant karyotype. Numerical chromosomal aberrations were determined in 51% samples. The most common aberration was trisomy 21 (67%). Structural chromosomal changes were detected in 49% samples. Leading one was a pericentric inversion of chromosome (75%) in rest of 26 samples balanced reciprocal translocation, was found in 58% of the samples and mostly inherited from the mother . Robertsonian translocation was found in 27% of amniotic fluid samples and was most commonly inherited from the mother, too. The leading indication among 217 examined samples with detected chromosomopathies was maternal age (59%), followed by the biochemical screening test of the second trimester (17%). The median age of the participants was 37 years (range 19 to 48 years), while the median gestational age was 17 weeks (range 11 to 28 weeks). The results indicate a significant decrease in the number of prenatal diagnostic samples which is most likely due to demographic circumstances, as well as development of more sensitive screening tests for aneuploidies and new methods of molecular karyotyping. However, conventional karyotyping still represents the gold standard, primarily for the detection of balanced structural changes, but also for detection of the mosaic karyotype with a low degree of mosaicism.