Determining the size of nanoparticles accurately, quickly and easily is becoming more and more important as the use of such particles increases. One of the common techniques for measuring the size of particles in suspension is dynamic light scattering (DLS). In principle, DLS is able to estimate the hydrodynamic particle diameter and its intensity-weighted distribution. However, the measured correlation function or power spectrum must be inverted to obtain this size distribution. The inversion is an ill-posed mathematical problem, and only under certain assumptions can the distribution be determined reliably. Suspensions containing bimodal (or multi-modal) particle size distributions are particularly challenging. This study reports on DLS measurements on a range of bimodal distributions of latex spheres with varying ratios of particle sizes. To determine the efficacy of different inversion techniques, the data has been analyzed both with the algorithms implemented in the DLS instrument's proprietary analysis software and with other inversion routines based on simple analytical models of the particle size distribution. In addition, the results of the DLS analysis have been compared to scanning and transmission electron microscopy (SEM and TEM) measurements. (C) Crown Copyright 2011 The Society of Powder Technology Japan. Published by Elsevier B.V. All rights reserved.