Strong size and internal density evolution of early-type galaxies between image and the present has been reported by several authors. Here we analyze samples of nearby and distant galaxies with dynamically measured masses in order to confirm the previous, model-dependent results and constrain the uncertainties that may play a role. Velocity dispersion ( capital sigma ) measurements are taken from the literature for 50 morphologically selected image field and cluster early-type galaxies with typical masses image. Sizes are determined with Advanced Camera for Surveys imaging. We compare the distant sample with a large sample of nearby early-type galaxies extracted from the Sloan Digital Sky Survey for which we determine sizes, masses, and densities in a consistent manner, using simulations to quantify systematic differences between the size measurements of nearby and distant galaxies. We find a highly significant difference between the image distributions of the nearby and distant samples, regardless of sample selection effects. The implied evolution in image at fixed mass between image and the present is a factor of image. This is in qualitative agreement with semianalytic models; however, the observed evolution is much faster than the predicted evolution. Our results reinforce and are quantitatively consistent with previous, photometric studies that found size evolution of up to a factor of 5 since image. A combination of structural evolution of individual galaxies through the accretion of companions and the continuous formation of early-type galaxies through increasingly gas-poor mergers is one plausible explanation of the observations.