The economic importance of livestock production has been undervalued compared to crop production and agricultural economists have not given it the attention which it deserves. Animal health is a significant influence on the productivity of livestock and the economics of animal husbandry. The range of animal health issues which can be usefully considered by economists is outlined. Some of the economic issues and problems involved in extrapolating farm-level and village-level estimates of the economic benefits of livestock disease control to the national level are outlined and discussed. The main problem is the possibility that aggregation or extrapolation of micro-data will fail to account for externalities, market changes dependant on aggregate production, such as variations in market price and changes in access to markets, such as export markets. Traditionally, cost-benefit analysis has been the most widely used technique for assessing the economics of control of animal diseases. It has been criticised by Mcinerney who suggests an alternative approach and this is considered. In conclusion, a brief outline is given of the Thai-Australian Animal Health Project (ACIAR Project 92804) which contains an economic component.