A fundamental understanding of how near-IR light propagates through sound and carious dental hard tissues is essential for the development of clinically useful optical diagnostic systems, since image contrast is based on changes in the optical properties of these tissues upon demineralization. The optical properties of enamel can be quantitatively described by defining the optical constants, the absorption and scattering coefficients, and the scattering phase function. Our aim was to measure the optical scattering properties of natural enamel caries. Near-IR attenuation measurements and angular-resolved goniometer measurements coupled with Monte Carlo simulations were used to determine the optical properties of natural lesions. An ultra-high resolution digital microradiography system was used to quantify the lesion severity by measurement of the relative mineral loss for comparison with optical scattering measurements. Natural demineralization increases the scattering coefficient more than two orders of magnitude at 1310-nm and the scattering is highly forward directed.