Statement of problem: It remains unclear which shade guide system is most representative of the shades found in the human dentition. Purpose: The purpose of this study was to determine and to compare the coverage errors (CEs) of 3 different shades in a selected population. Material and methods: The coverage errors of the following shade guide systems were evaluated to determine which shade guide system is most effective in producing the best visual shade match: (1) Vita Lumin, (2) Chromascop, (3) Vitapan 3D Master, and (4) a combination of the 3 shade guide systems. The spectral reflectance values of the central one ninth (1-mm diameter) of each shade tab (without a backing) were measured with a spectroradiometer and an external light source at wavelengths from 380 nm to 780 nm at 2-nm intervals. All spectral reflectance measurements were made using 0-degree observer and 45-degree illumination and then converted to CIE values. The color values of 359 anterior teeth were measured with the same protocol. The CEs for each of the 359 anterior teeth for each shade guide system, and with all 3 shade guide systems, were determined and averaged. Repeated measure ANOVA was used to evaluate the mean minimum CEs within-subject (shade guide system) and between-subject (age) difference as well as the interaction between these variables (α=.05). Then, a post hoc multiple comparison was performed using the Tukey-Kramer test. Results: A significant difference (P<.001) was found among the mean minimum CEs of the 3 shade guide systems and their combination, but not between age groups (P=.384). An interaction was found between shade guide systems and age (P<.001). The Tukey-Kramer test revealed that the mean minimum CEs for Vita Lumin (5.39 ΔE) and Chromoscop (5.28 ΔE) shade guide systems were not significantly different from each other. However, the combination of all 3 shade guide systems (3.69 ΔE) and Vitapan 3D Master (3.93 ΔE) were significantly different from the Vita Lumin and Chromoscop shade guide system. The rankings of the shade guide systems within each age group were similar between the age groups. Conclusions: The Vitapan 3D Master shade guide system resulted in the lowest coverage errors compared to the Vita Lumin or Chromascop shade guide systems. Coverage errors for the Vitapan 3D Master shade guide system did not differ significantly from the coverage errors when all 3 shade guide systems were combined. (J Prosthet Dent 2007;98:175-185).