OBJECTIVES: There is a wealth of literature and guidance available for cost-effectiveness research, but the guidance available on budget impact analysis (BIA) is less familiar to many investigators. In times of increased budget constraint, however, the importance and popularity of BIA is growing. The objective of this review was to assess whether guidance on BIA methodology is available and consistent. METHODS: Online searches were performed to identify published guidelines or recommendations on BIA from any country. The guidelines were then reviewed for whether they gave advice on certain pre-determined methodological categories. RESULTS: National guidelines have been produced in Canada, Ireland, Scotland and Poland specifically on how BIA in each of these countries should be performed. Other countries such as the UK, Italy and Hungary include recommendations on BIA within guidelines on health care economic assessment, but their focus is largely on cost-effectiveness analysis. The national guidelines were consistent in whether they made recommendations on perspective and time horizon, but varied in whether they gave advice on market share determination, sources of costs, inclusion of treatment of adverse events and the presentation of resource use and costs separately. The definition of the term ‘incremental BIA’ was also used inconsistently. An ISPOR Task Force has produced international guidance for budget impact methodologies, which is designed to support national guidelines rather than supersede them and also to improve consistency across BIAs developed for different settings. CONCLUSIONS: Several national and international bodies have developed guidelines or tools for developing and reporting budget impact models. However, different specifications exist and not all methodological aspects are made explicit in every case. Consensus guidelines such as those produced by the ISPOR task force are required to shape future national BIA recommendations.