Intracytoplasmic sperm injection (ICSI) is now established in the treatment of infertility. Fertilization is achieved by microinjection of a single spermatozoon into the ooplasma. Oligoasthenoteratozoospermia is the main indication, but ICSI is also used in cases of failed fertilization after standard IVF, retrograde ejaculation and male immunological infertility. In obstructive azoospermia ICSI is performed after aspiration of epididymal or testicular spermatozoa. In some anejaculatoric men spermatozon can be obtained following penile vibration or electro-stimulation, but they often have poor motility and ICSI may be used for fertilization. ICSI may also be used after thawing of semen cryopreserved prior to treatment of a malignant disease. Since 1991 the ICSI technique has been improved, and today the pregnancy rates are at least as good as after standard IVF. So far, studies of the foetuses and children born after ICSI show that the number of malformations and abnormal karyotypes is within the range of the normal population.