Dental shade guides contain a limited selection of colors compared to those found in human teeth. An error in shade selection is thus introduced, since many tooth colors must be defined by approximation to the nearest shade of the guide. The Bioform and Vita Lumin guides, and a combination of the two, were spectrophotometrically compared to the published colors of 335 human teeth. The minimum CIE L*a*b* color difference was calculated for each tooth using each shade guide. The average of these color differences was defined as the coverage error. The Bioform and Vita shade guide coverage errors were not significantly different, but the coverage error was significantly lower when the combination was used. The use of both guides in shade selection is recommended to reduce the coverage error.