This paper highlights the operational possibilities of applying non-parametric distance functions to diagnose farm performance. An empirical application on 178 farms in the Pas de Calais region specialized in field crops and observed over the period 1994-2001 establishes the coherence of this method compared to the usual approaches based on technical and accounting ratios. In addition, our results highlight the relevance of the additional information which is being generated by dissociating the technical and scale components of total factor productivity levels.