Rethore syndrome (trisomy 9p) is an inherited poly-malformation syndrome caused by chromosomal aberration. The authors describe the čase of a boy, where common cytogenetic methods revealed the presence of chromosomal aberration including chromosomes 9 and 11. The method of fluorescence in šitu hybdridization (FISH) and comparative genomic hybridization (CGH) revealed the presence of trisomy 9p in the formof isochromosome 9p. At the samé time, translocation of the long arm of 9q to chromosome 11 was confirmed. Karyotype of the proband was therefore: 46,XY, i(9)(P10),der(ll),t(9;ll)(ql3;q24).

        Key words: displayed a normál karyotype and the chromosomal aberration in the proband therefore developed "de novo". The risk of disease to be repeated in the family is negligible.