Chromosomal abnormality and Y chromosome microdeletion are regarded as two 
frequent genetic causes associated with spermatogenic failure in Caucasian 
population. To investigate the distribution of the two genetic defects in 
Chinese patients with azoospermia or severe oligozoospermia, karyotype analysis 
by G-banding was carried out in 358 idiopathic infertile men, including 256 
patients with azoospermia and 102 patients with severe oligozoospermia, and 
screening of AZF region microdeletion of Y chromosome by multiplex PCR was 
performed in those patients without detectable chromosomal abnormality and 100 
fertile controls. Of 358 patients, 39(10.9%) were found to have chromosomal 
abnormalities in which Klinefelter's syndrome (47, XXY) was the most common 
chromosomal aberration. The incidence of sex chromosomal abnormality in patients 
with azoospermia was significantly higher than that in patients with severe 
oligozoospermia (12.1% vs 1%). Among the rest of the 319 patients with normal 
karyotype, 46 (14.4%) were found to have microdeletions in AZF region. The 
prevalence rates of AZF microdeletion was 15% and 13.1% in patients with 
azoospermia and severe oligozoospermia respectively. The microdeletion in AZFc 
was the most frequent deletion and all the microdeletions in AZFa were found in 
azoospermic patients. No microdeletion in AZF region was detected in fertile 
controls. In conclusion, chromosomal abnormality and AZF region microdeletion of 
Y chromosome might account for about 25% of Chinese infertile patients with 
azoospermia or severe oligozoospermia, suggesting the two abnormalities are 
important genetic etiology of spermatogenic failure in Chinese population and it 
is essential to screen them during diagnosis of male infertility before in vitro 
assisted fertilization by introcytoplasmic sperm injection.