Pig farming is one of the strongest polluters of water due to its intensive production and slurry rejection. Several European countries have introduced environmental regulations aiming at reducing the pollution caused by nitrates from agriculture, but not yet Hungary. We investigate how Hungarian pig farms' output and technical efficiency would be affected if such regulations are to be fully implemented in this country. Results indicate that the pollution could be reduced with no impact on the output level, and that pig farmers have incentives to reduce nitrogen pollution in order to increase their efficiency even in the absence of regulation. Copyright © 2013 John Wiley & Sons, Ltd.