The objective of this study was to compare and analyse coding practices for diabetes mortality data in nine European countries (Belgium, Republic of Ireland, France, Germany, Malta, The Netherlands, Northern Ireland, Scotland and Switzerland). In each country, a sample of 200 coded death certificates, which mentioned diabetes, was randomly sampled. All death certificates were recoded at the WHO Collaborating Centre for the Classification of Diseases in the French language. The results show wide differences between national coding and central coding. Discrepancies in the underlying cause of death existed at the 3-digit coding level for 26% of all death certificates and for 44% at the 4-digit level. Coding in Northern Ireland and Malta was characterized by a marked tendency to choose diabetes less frequently. In contrast, in The Netherlands and, to a lesser extent, in the Republic of Ireland and France, diabetes was more frequently selected as the underlying cause of death. Most of the differences concerned the coding of an association involving diabetes and circulatory system diseases. In some countries, these coding differences influence the reported level of diabetes mortality. For Northern Ireland and Malta, the number of certificates with diabetes as the underlying cause of death was more than doubled after central recoding and for The Netherlands, in contrast, it was almost halved. To explain the differences a number of factors are considered: a lack of information from the Interna tional Classification of Diseases (lCD), on the application of the coding rules, between-country differences in cause of death certification practices, a divergence of opinion about the causal role of diabetes when it is associated with other conditions, a lack of homogeneity between countries in data collection procedures. Proposals are made to improve the collection and analysis of diabetes mortality data: in particular, the need to collect and analyse mortality data in terms of multiple-cause mortality for chronic diseases such as diabetes.