Infertility affects 10-15% of all couples and the male factor is responsible in approximately half of them. The advances in assisted reproduction techniques and genetic diagnoses have increased the percentage of couples who are able to conceive. We report on an infertile male patient with azoospermia, referred to our laboratory before intracytoplasmic sperm injection (ICSI), whose peripheral lymphocyte karyotype showed a 45, X/46, XY mosaicism. A Y chromosome (Yq) microdeletion was detected in the azoospermia factor (AZF) regions, AZFb and AZFc. The karyotype from testicular tissue cultures was mosaic 45, X[13]/47, XYY[12]/46, XY[25]. Fluorescence