OBJECTIVES: Underlying the success of multi-country cost of illness studies are the methods used to identify, enumerate and value the resources that constitute the overall costs of the disease being studied. The design objective of the data collection instruments is to ensure consistency between countries and retrieval of all relevant data. METHODS: The CODE-2* (Costs of Diabetes in Europe type 2) study is a bottom-up, prevalence based cost of illness study conducted to evaluate the total burden of type 2 diabetes in 8 European countries. The objective of the study was to fully identify all costs relating to the management of the disease and its associated complications in addition to patient demographic and clinical parameters. Data for over 7000 patients were collected retrospectively over a 6-month period from a variety of sources including patient interviews, medical records and registries. This required the design of common data collection tools that could be used in all eight countries by over 600 practitioners included in the study. Identification of core items of resource utilisation and clinical assessments was done in consultation with European and national advisory boards consisting of health economists, clinicians and healthcare researchers. A process of forward and back translation ensured the cultural and linguistic integrity of the eight language versions used. Layout and instrument design were developed by iteration between the central study coordinating and country teams and assessed by mini-pilots. Final field tests ensured acceptability and suitability for study participants. RESULTS: The resulting country specific practitioner and patient data collection instruments were consistent in all aspects for core resource utilisation items necessary for inter-country comparison of the study results. CONCLUSION: The instruments and development process used for the CODE-2 study should serve as a model for other multi-country cost of illness studies. *Registered Trademark of SmithKline Beecham