STUDY QUESTION:What was the impact on access to assisted reproductive technology (ART) treatment by different socioeconomic status (SES) groups after the introduction of a policy that increased patient out-of-pocket costs? SUMMARY ANSWER:After the introduction of a policy that increased out-of-pocket costs in Australia, all SES groups experienced a similar percentage reduction in fresh ART cycles per 1000 women of reproductive age. Higher SES groups experienced a progressively greater reduction in absolute numbers of fresh ART cycles due to existing higher levels of utilization. WHAT IS KNOWN ALREADY:Australia has supportive public funding arrangements for ARTs. Policies that substantially increase out-of-pocket costs for ART treatment create financial barriers to access and an overall reduction in utilization. Data from the USA suggests that disparities exist in access to ART treatment based on ethnicity, education level and income. STUDY DESIGN, SIZE, DURATION:Time series analysis of utilization of ART, intrauterine insemination (IUI) and clomiphene citrate by women from varying SES groups before and after the introduction of a change in the level of public funding for ART. PARTICIPANTS/MATERIALS, SETTING, METHODS:Women undertaking fertility treatment in Australia between 2007 and 2010. MAIN RESULTS AND THE ROLE OF CHANCE:Women from higher SES quintiles use more ART treatment than those in lower SES quintiles, which likely reflects a greater ability to pay for treatment and a greater need for ART treatment as indicated by the trend to later childbearing. In 2009, 10.13 and 5.17 fresh ART cycles per 1000 women of reproductive age were performed in women in the highest and lowest SES quintiles respectively. In the 12 months after the introduction of a policy that increased out-of-pocket costs from ∼$1500 Australian dollars (€1000) to ∼$2500 (€1670) for a fresh IVF cycle, there was a 21-25% reduction in fresh ART cycles across all SES quintiles. The absolute reduction in fresh ART cycles in the highest SES quintile was double that in the lowest SES quintile. LIMITATIONS, REASONS FOR CAUTION:In this study, SES was based on the average relative socioeconomic advantage and disadvantage of small geographic areas, and therefore may not reflect the SES of an individual. Additionally, the policy impact was limited to the 12 months following its introduction, and may not reflect longer term trends in ART treatment. WIDER IMPLICATIONS OF THE FINDINGS:While financial barriers are an important obstacle to equitable access to ARTs, socioeconomic differences in utilization are likely to persist in countries with supportive public funding, due in part to differences in childbearing patterns and treatment seeking behaviour. Policy makers should be informed of the impact that changes in the level of cost subsidization have on access to ART treatment by different socioeconomic groups. STUDY FUNDING/COMPETING INTEREST(S):G.M.C. receives grant support to her institution from the Australian Government, Australian Research Council (ARC) Linkage Grant No LP1002165; ARC Linkage Grant Partner Organisations are IVFAustralia, Melbourne IVF and Queensland Fertility Group. V.P.H. is employed as an Economics Research Associate on the same grant. P.J.I. is Medical Director of the IVF Clinic, IVFAustralia and has a financial interest in the parent group, Virtus. TRIAL REGISTRATION NUMBER:N/A.