This study contributes to the literature on the performance of diagnosis-related groups (DRGs) for acute myocardial infarction (AMI) patients by evaluating in nine countries the factors—in addition to DRGs—that affect costs or length of stay and comparing the variation that can be explained with or without DRGs. We evaluate whether the existing DRGs for AMI patients would benefit from additional patient-related and treatment-related factors that are found in administrative data across countries. In most countries, the set of patient and quality variables performed better than the DRG variables. Our results suggest that DRG systems in all countries could be improved by including additional explanatory factors or by refining the existing DRGs. Our results suggest that for AMI and possibly for other related episodes, a refinement of DRGs to include information on patient severity, procedures and levels of complications could improve the ability of DRGs to explain resource use. It seems possible to improve DRG-like hospital payment systems through the inclusion of episode-specific variables. Copyright © 2012 John Wiley qqqamp; Sons, Ltd.