In tolerancing activity, surfaces are usually considered without any defects (i.e. no waviness and no rugosity). Consequently, only size and position defects of surfaces are taken into account. The focus of this paper is to show the importance of these surface defects on assembly; it is highlighted that even if the real surface respects the geometrical specifications, it is possible to have a non-conform assembly. The developed method is applied on an assembly which uses two carters composed in parallel of a ball and cylinder pair and of a planar pair.