The relationship between crystal population density and chord-length density (CLD) is complicated and depends on the size and shape of the crystals. Although estimation of chord-length density from the population density is relatively straightforward, the inversion of this procedure is problematic because the problem may be ill-conditioned for nonspherical particles. The focus of this work is on this inversion process. Since the relationship is a function of the crystal geometry, this manuscript considers various nonspherical shapes, including highly challenging needles. We describe an efficient method to estimate the population density from a measured CLD, to analyze the inversion process, and to quantify its limits. Since noise is present in the actual Focused Beam Reflectance Measurements, the case of restoration of the population density from noisy CLDs also is demonstrated. (C) 2009 American Institute of Chemical Engineers AIChE J, 55: 2260-2270, 2009