We discuss a density functional approach of non-uniform electrolytes that includes the term that takes into account the formation of associated ionic pairs. The theory is based on a fundamental measurement theory of hard-spheres, the theory of Gillespie et al. [D. Gillespie, W. Nonner, R.S. Eisenberg, J. Phys.: Condens. Matter 14 (2002) 12129] which leads to a more accurate description of the electrostatic part of the grand potential and on the Wertheim theory of association. The results of model calculations indicate that at low temperatures the inclusion of the associative term in the grand potential leads to the structure of the double layer, which differs from the structure evaluated by neglecting the association. However, these differences become negligibly small at high temperatures. (C) 2004 Elsevier B.V. All rights reserved.