STUDY QUESTION: Have changes in assisted reproductive technology (ART) practice and outcomes occurred globally between 2003 and 2004? SUMMARY ANSWER: Globally, ART practice has changed with an increasing prevalence of the use of ICSI rather than conventional IVF. In 2004, a small but increasing number of countries are incorporating single embryo transfer. There remain unacceptably high rates of three or more embryo transfers in select countries resulting in multiple births and adverse perinatal outcomes. WHAT IS KNOWN ALREADY: World data on the availability, effectiveness and safety of ART have been published since 1989. The number of embryos transferred is a major determinant of the iatrogenic increase in multiple pregnancies and is highly correlated with the likelihood of multiple birth and excess perinatal morbidity and mortality. STUDY DESIGN, SIZE, DURATION: Cross-sectional survey of countries and regions undertaking surveillance of ART procedures started in 2004 and their corresponding outcomes. PARTICIPANTS/MATERIALS, SETTING, METHODS: Of total, 2184 clinics from 52 reporting countries and regions. Number of ART clinics, types of cycles and procedures, pregnancy, delivery and multiple birth rates and perinatal outcomes. MAIN RESULTS AND THE ROLE OF CHANCE: A total of 954 743 initiated cycles resulted in an estimated 237 809 babies born. This was a 2.3% increase in the number of reported cycles from 2003. The availability of ART varied by country and ranged from 14 to 3844 treatment cycles per million population. Over one-third (37.2%) of ART clinics performed <100 cycles per year with only 19.9% performing ≥ 500 cycles per year. Of all cycles, 60.6% were ICSI. Frozen embryo transfers (FETs) represented 31% of the initiated cycles. The overall delivery rate per fresh aspiration for IVF and ICSI was 20.2% compared with 16.6% per FET. The average number of embryos transferred was 2.35. Single (16.3%) and double embryo transfers accounted for 73.2% of cycles. The overall proportion of deliveries with twins and triplets from IVF and ICSI was 25.1 and 1.8%, respectively, but varied widely by country and region. The proportion of premature deliveries per fresh aspiration for IVF and ICSI was 33.7% compared with 26.3% per FET. The perinatal death rate was 25.8 per 1000 births for fresh aspiration for IVF and ICSI compared with 14.2 per 1000 births per FET. LIMITATIONS, REASONS FOR CAUTION: Data are incomplete with seven countries not providing data to the International Committee for Monitoring Assisted Reproductive Technologies (ICMART) in 2004 that had in 2003. The validity of data reflects current data collection practice. In 2004, 79.3% of the clinics in participating countries reported to their national or regional registries and to ICMART. In addition, the number of ART cycles per million population is a measure which is affected by a country's government policy, regulation, funding and the number of service providers. WIDER IMPLICATIONS OF THE FINDINGS: ART practice, effectiveness and outcomes vary markedly internationally. Notably, the increasing proportion of cycles that are FET, the change in practice to single embryo transfer and the cessation of the transfer of three or more embryos in some countries has resulted in improved perinatal outcomes with minimal impact on pregnancy rates. STUDY FUNDING/COMPETING INTEREST(S): ICMART receives financial support from ASRM, ESHRE, FSA, Japan Society for Reproductive Medicine, REDLARA, MEFS and SART.