Tooth color is determined by the paths of light inside the tooth and absorption along these paths. This paper tests the hypothesis that, since the paths are determined by scattering, a relation between color and scattering coefficients exists. One hundred and two extracted incisors were fixed in formalin, mounted in a standardized position in brass holders, and pumiced. A facet was prepared near the incisal edge on the labial plane to allow for Knoop hardness measurements with a 500-gram load. Light scattering by the enamel was measured in a 45 degrees/0 degrees geometry; light scattering by both enamel and dentin was measured in a 0 degrees/0 degrees geometry. The reflection spectrum of the tooth was measured from the labial plane with a spectroradiometer in a 45 degrees/0 degrees geometry, with standard illuminant A and standard illuminant D65. To include all volume-reflected light, we used entire-tooth illumination and small-area measurement. CIELAB color coordinates were calculated from the spectra. Neither spectra nor coordinates showed evidence of a contribution of fluorescence to tooth color. Averaged values and standard deviations for L*,a*,b* were 69.9 (4.1), 1.22 (1.4), and 17.9 (2.9), respectively. Both scattering coefficients averaged to 0.6 (0.4) mm-1; Knoop hardness number was, on average, 271 (39) kg/mm2. L* correlated with a* (r = -0.51), with the enamel scattering coefficient (r = 0.60), and slightly with hardness (r = 0.17, p = 0.03). The colors of 28 teeth from which the enamel was removed correlated strongly with the colors of the complete tooth.(ABSTRACT TRUNCATED AT 250 WORDS)