Recently, several studies compared the performance of conventional and organic farms. Most studies concentrated on technical efficiency. In this paper we add to this literature by also comparing the scale efficiency of conventional and organic milk farms in Austria during the period 1997-2002. To do so we utilize a bilateral production frontier that includes both production technologies and Green’s (1995a,b) true fixed effects model to account for firm specific time-invariant heterogeneity and technical inefficiency. We find both groups of farms to be on average equally technical efficient (when compared to their production frontier), but conventional farms being on average considerably more scale efficient. However, while scale efficiency remained constant over time for conventional farms it increased for organic farms which seem to catch up.