The aim of the study was to determine the rate of chromosome abnormalities in testicular sperm after intracytoplasmic sperm injection due to severe male factor infertility. The study groups included patient with non-obstructive azoospermia (n=9), obstructive azoospermia (n=10), Klinefelter's syndrome (n=5) and normal controls (n=6, groups I-VI, respectively). The mean serum levels of FSH 17.5+/-8.2 (P<0.05), 3.5+/-2.6, 29.8+/-13.0 (P<0.05) and 3.1+/-0.4 mIU/ml, respectively. The rates of chromosome abnormalities were 19.6% (P<0.001), 8.2% (P<0.001), 6.3 and 1.6%, respectively. Chromosomes X and Y were significantly more involved in the aneuploidy than chromosome 18 in groups I and II. The present findings demonstrate a linkage between gonadal failure (high serum FSH levels) and sperm chromosome abnormalities. Our findings may explain the increased incidence of perinatal sex chromosome abnormalities found in severe male factor patients. Patients with non-mosaic Klinefelter's syndrome have comparable risk for sex chromosomes aneuploidy as the rest of the patients with azoospermia. Therefore, genetic screening during pregnancy or before embryo replacement should be carefully considered in severe male factor patient following in vitro fertilization (IVF).