en Original Article Original Article <strong>Background:</strong> Cytogenetic analysis, Y-chromosome microdeletion screening, FISH techniques and other genetic methods have helped in finding the causes of infertility in azoospermic or severe oligoazoospermic cases in the last decade.<br> <strong>Objective:</strong> In the present study, we characterized an abnormal Y-chromosome, detected as a mosaic in an azoospermic male ascertained for infertility. <strong>Materials and Methods:</strong> Chromosome analysis, using G, Q and C banding techniques and FISH analyses with several different DNA probes specific for Y and X chromosome sequences [XY centromeric &alpha;-satellite, Y non-&alpha;-satellite III, LSI-probes of the Y chromosome, WCP of Chromosome Y, SRY gene, subtelomeric Xp and Yp, which cover the SHOX (short stature-homeobox containing) gene, and subtelomeric Xq and Yq probes] were performed. A total of 20 sequence tagged sites were analyzed using primer sets specific for the Y-chromosome microdeletion loci. The primers were chosen to cover AZFa, AZFb, and AZFc regions as well as the SRY gene.<br> <strong>Results:</strong> Chromosome analysis revealed a gonosomal mosaicism of monosomy X (51%) and a pseudodicentric Y (49%) chromosome: mos 45, X/46,X psu dic (Y) (qter&rarr;p11.32 :: p11.2&rarr;qter). Molecular genetic studies did not show deletions in the AZFabc regions, but a deletion was found in the short arms of the dicentric Y chromosome. One of the SRY genes was also missing.<br> <strong>Conclusion:</strong> The azoospermia in this patient could be explained by either the presence of an abnormal Y-chromosome that cannot form a sex vesicle (which appears to be necessary for the completion of meiosis process and the formation of sperm), or the presence of the 45, X cell line. Dicentric Y chromosome, Dic (Yq), FISH, Mosaicism, Azoospermia 57 0 http://ijrm.ir/browse.php?a_code=A-10-549-242&slc_lang=en&sid=1 Mir Davood Omrani davood_omrani@umsu.ac.ir Yes Department of Genetics, Urmia Medical Sciences University, Iran Javad Karimzad Hagh No Institute of Human Genetics and Anthropologia, Heinrich-Heine-University of Düsseldorf, Germany Wolfrom Klein No Department of Human Genetics, Ruhr- University Bochum, Germany Jurgen Gebauer No Institute of Human Genetics and Anthropologia, Heinrich-Heine-University of Düsseldorf, Germany