The increased risk of perinatal and infant mortality observed among in vitro fertilisation (IVF) births and other assisted conception births is thought to be largely attributable to multiplicity. Using mortality statistics and estimates of the proportion of births following infertility treatment, we predicted the excess stillbirths and infant deaths associated with twins and higher order births resulting from assisted conception in England and Wales. According to our results, approximately 73 deaths could have been avoided in 2001 if all IVF infants had been born as singletons or as naturally occurring monozygotic twins, equating to a population attributable risk fraction of around 1% for perinatal and infant deaths. If we include all types of assisted conception, this figure was estimated to be around 4% of deaths—more than 220 perinatal and infant deaths in 2001. We confirm the public health importance of multiple births associated with assisted conception.