Saccharin (o-benzoic sulfimide) preferentially adsorbs onto platinum(111)electrodes modified with the (3x3) iodine adlayers (theta(1) = 0.44). This is in contrast to platinum (111) electrodes modified with the (root 7x root 7)R19.1 degrees iodine adlayer (theta(1) = 0.43) where no adsorption is detected. Saccharin adsorption was monitored through changes in the voltammograms associated with the oxidative desorption of the strongly bound iodine adlayer and Ag underpotential deposition on the iodine-modified electrode surfaces in acidic solutions. Simple modeling calculations support the experimental observation and suggest that the preferential adsorptive behavior of saccharin is due to the enhanced van der Waals interactions associated with the symmetric Pt(111)(3x3)-I adlayer structure. The Pt(111)(3x3)-I adlayer structure is one of two (3x3) iodine adlayer structures found to a comparable extent of coverage on name-annealed Pt(111) electrodes exposed to iodine for a longer duration than that leading to the formation of the Pt(111)(root 7x root 7)R19.1 degrees-I adlattice.