A budget impact analysis (BIA) is used to assess whether the adoption of a new health technology is affordable, given the resource and budget constraints of the context. Increasingly, BIAs are coming to be viewed as an important-if not essential-part of health technology assessment (HTA). BIA data is often examined in conjunction with cost-effectiveness analysis (CEA) data to help inform decisions makers when developing reimbursement policies within the resource constraints of their health care system. This article presents a review of existing BIA guidelines from around the world and makes some initial recommendations for the development of Thai BIA guidelines, as part of the newly-developed Economic Evaluation guidelines for Thailand. Initial recommendations include guidelines on appropriate analytic framework design, study design, perspective, scenarios for comparison, target population, costing and resource use, uncertainty analysis, and discounting.