In France, the second national survey on health and disability, carried out in 2008-2009, is the main data source dealing with the disability process and concerning the whole population living either in institutions or in ordinary households. Following WHO's recommendations to use jointly the ICD and the ICF in surveys, the questionnaire was designed to investigate two planes of experience, close but distinct: diseases on one hand, impairments on the other. While promoting a complete analysis of the disabling processes, nevertheless this approach raises some difficulties, especially in the field of mental health. This article aims at identifying the reasons and challenges as well as the benefits and limits of this twofold investigation. It intends also to examine its concrete consequences, on the basis of a qualitative survey carried out among 44 respondents to the questionnaire who had declared having mental difficulties in both categories of experience. The way respondents differentiate disease and impairment when answering questions related to anxiety and mood suggests avenues for further reflection on the criteria people use to specify their difficulties in one plane of experience or the other. © 2015 Association ALTER