Male infertility can be caused by Y chromosome microdeletions. The knowledge of Y chromosome microdeletions in infertil men is important for medical assisted reproductive methods, because genetically determined male infertility would be transmited to the male offspring by the Y chromosome. We analyzed 270 unselected patients with indication for an intracytoplasmic sperm injection treatment on deletions of the DAZ gene complex in the AZFc region of the long arm of the Y chromosome. Furthermore we examined the frequencies for the 5T-, 7T- and 9T alleles of the thymidine sequence polymorphism in intron 8 of the CFTR gene in 218 ICSI patients in order to check a possible correlation with the sperm concentration. We found two (0,75%) identical AZFc deletions in the ICSI collective (n=270). Both had severe disturbance of the spermatogenesis (azoospermic and cryptozoospermic). One patient had a hypospadia glandis. Subdividing the ICSI collective in groups shows, that the prevalence of AZFc deletions in azoospermic patients is 7,7% and 5% in patients with cryptozoospermia (6 spermatozoa/ml ejaculate). In patients with more than 1x106 spermatozoa/ml ejaculate no deletion were found. The frequencies of the 5T-, 7T- and 9T-alleles in the ICSI collective (5T: 3,7%, 7T: 85,2%, 9T: 11,1%) were not different from a reference group. Subdividing the ICSI collective in groups shows a significant higher prevalence (p=0,02) of the 5T allele in the azoopsermic group compared with the reference group. An analysis of the frequencies of CFTR and chromosome mutations shows a higher prevalence of chromosome mutations (2,7%) in the ICSI collective than in the normal population. This is a result from a very high significant (p<0,01) prevalence of chromosome mutations (8%) in the normozoospermic group of the ICSI patients. The rate of CFTR mutations detected (4,1% ) was not increased in the whole ICSI collective compared with the normal population. An analysis in subgroups again shows a high significant (p<0,01) prevalence in the normozoospermic group. In summary the prevalence of AZFc deletions in ICSI patients with azoospermia and cryptozoospermia is up to 7,7%. In azoospermic ICSI patients the prevalence of the 5T allele is higher than in the normal population. The prevalence of CFTR und chromosome mutations in normospermic ICSI patients is higher than in the normal population.