Volume 17, Number 1Case ReviewRare Case of Monozygotic Twins Diagnosed With Klinefelter Syndrome During Evaluation for InfertilityEdmund S SabaneghYagil BarazaniAlthough neither Klinefelter syndrome nor monozygotic twins are particularly rare (1/667 male births and 3-4/1000 live births, respectively), the occurrence of both in the same pregnancy (ie, identical twins with Klinefelter syndrome) is exceedingly rare and has only been reported three times previously in the literature. This report describes the fourth ever reported case of monozygotic twins with Klinefelter syndrome (who presented to our male fertility clinic with failure to conceive) and sheds interesting light on the reproductive concordance observed with this rare clinical entity. To our knowledge, this is the first reported case of monozygotic twins with Klinefelter syndrome that describes the infertility workup and outcomes of microsurgical testicular sperm extraction. [Rev Urol. 2015;17(1):42-45 doi: 10.3909/riu0628] © 2015 MedReviews®, LLCKlinefelter syndromeMicrosurgical testicular sperm extractionAzoospermiaSertoli only syndromeGerm cell aplasia