This paper reviews the economic performance of Irish dairy farms over the period 1998 to 2006. Econometric techniques are employed to examine the variation in cost structures and to identify the factors affecting farm profitability. The overall objective of the paper is to establish the long term sustainability of dairy farming in Ireland and to explore the ability of farmers to cope with the potential price volatility that may arise out of a WTO agreement or reforms to the EU milk quota regime. National Farm Survey data from Ireland are used to analyse production costs. Average cost curves are shown for the Irish dairy industry and are compared to the results of similar analysis conducted for England and Wales.