Aim:To report a birth after intracytoplasmic sperm injection (ICSI) of ejaculated spermatozoa from a man withmosaic Klinefelter’s syndrome detected by fluorescence in situ hybridization (FISH) analysis.Methods:A 35-year-old man with a normal appearance consulted our hospital because of sterility over a 5-year period.Chromosomeanalysis showed low-incidence mosaic Klinefelter’s syndrome.Using FISH,96 % hyperploidy of the lymphocyteswas found.We examined the sex chromosome of the ejaculated spermatozoa.Using FISH,we examined 200 ejacu-lated spermatozoa and no hyperploidy was found.Results:The 33-year-old female partner of the male patientunderwent an uncomplicated controlled ovarian hyperstimulation sequence using a combined recombinant-folliclestimulating hormone (rec-FSH) + human menopausal gonadotrophin (hMG) protocol,following late luteal phasepituitary down regulation.This culminated in the retrieval of seven oocytes,six of which were fertilized with ICSI.One ICSI attempt led to clinical pregnancy with a healthy baby girl.Conclusion:We report a male patient with low-incidence mosaic Klinefelter’s syndrome whose ejaculated spermatozoa were identified as being haploid by FISHbefore ICSI,leading to the successful pregnancy of his wife and the birth of a healthy baby girl. Aim: To report a birth after intracytoplasmic sperm injection (ICSI) of ejaculated spermatozoa from a man with mosaic Klinefelter’s syndrome by fluorescence in situ hybridization (FISH) analysis. Methods: A 35-year-old man with normal appearance consulted our hospital because of sterility over a 5-year period. Chromosomeanalysis showed low-incidence mosaic Klinefelter’s syndrome. Using FISH, 96% hyperploidy of the lymphocyteswas found. We examined the sex chromosome of the ejaculated spermatozoa. Using FISH, we examined 200 ejacu-lated spermatozoa and no hyperploidy was found. Results: The 33-year-old female partner of the male patientunderwent an uncomplicated controlled ovarian hyperstimulation sequence using a combination recombinant-folliclestimulating hormone (rec-FSH) + human menopausal gonadotrophin (hMG) protocol, following late luteal phasepituitary down regulation. This culminated in the retrieval of seven oocytes, six of which were were fertilized with ICSI. One ICSI attempt led to clin ical pregnancy with a healthy baby girl. Confidence: We report a male patient with low-incidence mosaic Klinefelter’s syndrome whose ejaculated spermatozoa were identified as being haploid by FISHbefore ICSI, leading to the successful pregnancy of his wife and the birth of a healthy baby girl .