OBJECTIVES: As part of a health technology assessment comparing a single-embryo-transfer (SET) in In-Vitro Fertilization (IVF) with the traditional double-embryo-transfer (DET) used today in Denmark the cost-effectiveness of SET was compared with DET. The aim was to inform decision-makers about the economic consequences of the eventual adoption of a SET policy in Denmark. METHODS: The analysis was based on prospective collection of resource use and costs of singletons and twins. A total of 213 pregnant women at the fertility clinic have been reporting resource use (healthcare and so-cial sector), and days absent from work in cost diaries during a year (from pregnancy scan to until three months after delivery). Clinical effectiveness data of SET and DET came from a Scandinavian multi-center trial, and a recent Cochrane review. RESULTS: The advantage of SET is delivery of few expensive twins compared with DET (25%). The cost-effectiveness per clinical pregnancy of DET (DKK 115,321 per clinical pregnancy and DKK 120,934 per delivery) was lower than using that of SET (DKK 131,446 per clinical pregnancy and DKK 149,833 per delivery). The cost-effectiveness of DET is explained by a higher clinical pregnancy rate, a higher rate of delivery, and more children born. However, DET is also a more expen-sive alternative for the average patient treated, because of higher costs for delivery and neonatal care. The extra cost per patient using DET is around DKK 82,000 per delivery and around DKK 50,000 per extra child born using DET. CONCLUSION: The cost per delivery and per child born is lower using DET compared with SER. However, the total costs for DET is higher due to higher antenatal, delivery and neonatal costs, as well as production loss. A higher rate of twin deliveries using DET explains this. These extra costs using the more effective DET policy are moderate.