A hybrid density functional theory method previously developed for heterogeneous silica surfaces has-been used to calculate model isotherms over a wide range of pore widths for the adsorption of nitrogen at 77 K within cylindrical pores having a clay-like surface. Using these models and the experimental isotherm data, the integral equation of adsorption was inverted by a regularization method to yield the micropore and mesopore size distribution of a pillared interlayered clay (PILC). The results obtained are compared with the results of more traditional data treatments.