OBJECTIVES: Real world data studies provide a level of granularity that may be not be available in randomized clinical trials (RCTs) that have strict inclusive exclusion criteria and may lead to weak external validity.  Furthermore, RCTs generally do not capture important information on adherence, costs and rare side effects.  The purpose of this study is to understand how to design patient registries and other observational studies to optimize their use to support market access decisions. METHODS: First, secondary research was conducted by analysing existing registries in a given therapeutic area in European markets including Belgium, Denmark, France, Germany, Italy, Poland, Spain, Sweden and the United Kingdom.  Data points from existing registries were charted from ‘most’ to ‘least prevalent’.  Missing attributes that were perceived as essential based on expert opinion were also collected, identifying gaps in available data. Second, an international payer panel completed a quantitative survey and completed primary in depth interviews to understand the relative impact of all the registry attributes, including those that were perceived as gaps.  This included impact on price, reimbursement status and formulary listing.  Transferability of data was also tested to identify whether payers would accept data from other markets and determine what should be collected to maximise market access.   RESULTS: Data gaps were cross referenced with the payer needs to understand which endpoints are not currently being addressed.  This allowed an accurate map of critical endpoints needed to have the greatest impact on market access. CONCLUSIONS: In an era of evidence based medicine and constrained budgets, drug manufacturers need to identify how to best utilise real world data and patient registries.   Using this methodology, it is possible to identify what data to collect and where it should be collected in order to maximise the market access opportunity and pricing potential.