Purpose: This study evaluated the ability of five elastomeric impression materials to penetrate the gingival sulcus beyond the preparation margin. Materials and Methods: A model of brass and agar gel was made to simulate human sulci and clinical gingival conditions. Two addition-curing silicones, one condensation-curing silicone, one polyether, and one polysulfide were tested. Ninety impressions of the model were made, six impressions with each material with differing sulcular widths. The centers of sulcular extension of these impressions were found with a measuring microscope. Results: Two-way ANOVA showed significant differences among impression materials, sulcular widths, and their interactions. The penetration ability of polyether showed greater extension than the other materials, regardless of sulcular width. Polysulfide penetrated less than the two silicones with 0.2- and 0.1-mm sulcular widths but more with the narrow 0.05-mm sulcular width. Conclusion: These results suggest that the viscoelastic behavior of elastomers depends on the width of sulci. Moreover, the sulcus simulation model effectively contributes to the investigation of their characteristics. Int J Prosthodont 2003;16:385–389.