A newly developed procedure for estimating ice cloud effective particle size using combined lidar and radar signals has been applied to several months of data from the Atmospheric Radiation Measurement Program's Southern Great Plains site. Though considerable scatter is present in the retrieval results, on average, the data show a clear dependence of effective particle size on both temperature and ice water content. The data are used to construct a parameterization based on a bimodal ice particle size distribution whose characteristics depend both on temperature and ice water content.