The Danish IVF Register was established in 1994 and covers all treatments with in vitro fertilisation (IVF), intracytoplasmatic sperm injection (ICSI), frozen embryo replacements (FER) and egg donations (ED). Since data are recorded with personal identification numbers, they provide the starting point for cohort studies of treated women and offspring. It is obligatory for each clinic to report each treatment cycle to the register, by means of special treatment report forms that contain clinical as well as laboratory data. The pregnancy outcome is reported on special forms no later than two months after birth. The personal identification number (CPR) allows cross-linkage of the data from the register, with several other national Danish registers, such as the National Hospital Register the Abortion Register, the Danish Register of Causes of Death, the Cytogenetic Central Register and the Cancer Register. In 1998 a total of 7131 IVF and ICSI cycles were performed in Denmark. This corresponds to around 6500 cycles per 1 million women in the reproductive age, which is among the highest number per capita in the world. The coverage of the register is believed to be very close to 100% for the treatment reports, but less for the pregnancy outcome forms, at least during the first two years after the register was established. The main importance of the register is quality control aspects of assisted reproductive techniques and research in relation to follow-up on maternal and infant health.