One of the most problematic issues of assisted reproduction is the high incidence of multiple pregnancies, resulting from the transfer of more than one embryo. Particularly at risk are young women who have good quality embryos. The only strategy to reduce the incidence of multiple pregnancies, including twin pregnancies, after assisted reproduction is single embryo transfer (SET). In 1997, the present authors therefore introduced elective SET (eSET) in this particular target group. The proportion of eSET increased from 1.5 (1997-1998) to 17.5% (1999-2002) of all transfers. In 2002, 20% of all transfers were SET. Comparing these two periods, an overall pregnancy rate of 35 and 34% per transfer, respectively, was obtained, while the overall twinning rate dropped from 30 to 21%. The twinning rate dropped to 14% in 2002, and in the eSET group there was only one monozygotic twin. These results demonstrate that a decline in the twinning rate is feasible without a drop in overall pregnancy rates. Comparing eSET with elective double embryo transfer (eDET), it was found that ongoing pregnancy and implantation rates were the same in both groups, but the proportion of twins was clearly different. It was further observed that the mean birthweight of singleton children born after eSET was significantly higher than that after DET. This could reflect a better developmental or implantation potential of these embryos, but this finding remains to be confirmed.