This paper investigates the determinants of nitrogen surplus and of its two components-nitrogen intensity and nitrogen-inefficiency- at farm level in Swiss agriculture. Our analysis is based on a cross-section of 210 farms from the eyar 2010. The nitrogen balance of each farm is estimated according to the OECD soil-surface approach. The determinants are analysed by means of a three-equartion regression model estimated using a robust SUR approach. Farm size, part-time farming, organic farming, arable cropping and farmer's age are found to negatively affect nitrogen surplus, whilst dairy, pig and poultry farming are associated with a higher nitrogen surplus.