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The largest proportion of all chromosomal anomalies in humans are syndromes Down (trisomy of chromosome 21), Edwards (trisomy of chromosome 18) and Patau (trisomy of chromosome 13). This fact has revealed the need to introduce methods that would allow rapid diagnosis of the most common numerical chromosomal abnormalities, which is of special importance in prenatal diagnosis. Analysis of the microsatellite or STR locus with the PCR-STR method has given us the possibility of fast diagnosis of the most frequent aneuploidies within one to three days. The advantage of the analysis of STR loci in prenatal and postnatal diagnosis lies in the ability to determine the origin of chromosomes in the diagnosis of uniparental disomy. At the Zagreb University Hospital Centre, rapid prenatal and postnatal diagnosis of aneuploidy and uniparental disomy was performed using analysis of the microsatellite loci of chromosomes 7, 11, 13, 14, 15, 18, 21, X and Y. The purpose of the work was to show diagnostic value of the microsatellite loci on the above listed chromosomes. On prenatal screening of 2072 amniotic fluid samples, 55 (2.65%) showed change in the number of chromosomes. As expected, the largest number of samples (n=35) showed trisomy of chromosome 21. Uniparental disomy of chromosome 15 (UPD15) was demonstrated in 13 of 54 subjects with suspicion of uniparental disomy. The results of the PCR-STR method were in accordance with the results of conventional cytogenetics. In conclusion, the combination of STR loci that we use is considered good enough to determine aneuploidy of chromosomes 13, 18, 21, X and Y, and uniparental disomy of chromosomes 7, 11, 14 and 15. [ABSTRACT FROM AUTHOR]