The presence of an isochromosome Xq in Klinefelter syndrome is an apparently rare condition. In this report, the authors describe a rare case of isochromosome Xq [47,XY,i(X)(q10)] in a non - mosaic Klinefelter syndrome patient who is 26 years old with infertility. Semen analysis revealed a azoospermia and low serum testosterol level. The patient exhibited medium height (160 centimeters), small testes and phimosis, but showed no signs of intellectual disability.