There has been a continuous evolutionary process in hot-mix asphalt (HMA) pavement design. In the beginning it was primarily based on past experience. Through research, empirical methods were developed on the basis of the materials' response to specific loading in the AASHO Road Test. Today pavement design has progressed to a mechanistic- empirical method. This methodology takes into account the mechanical properties of the individual layers and uses empirical relationships to relate material properties to performance. The mechanical tests that are used as part of the current methodology include dynamic modulus and flow number, which have been shown to correlate with field pavement performance. The use of the dynamic modulus test and its impact on pavement design with the current design guide (2002) and its associated software are examined here. The three pavement structures that are examined were derived from the 1972 AASHTO design guide approach and were constructed in Wisconsin during the 2004 construction season. Through iterative changes in the HMA layer thickness, the major distresses of permanent deformation and fatigue were examined. Included in the examination were changes in air voids and asphalt binder content over ranges that were believed to be typical of HMA production and paving. All three pavements were predicted to perform well in terms of permanent deformation for the as-designed layer thicknesses. The 2002 design guide software, however, indicates that two of the three pavements considered may be prone to fatigue cracking, specifically at higher air void contents (+7.0%).