During the EASOE campaign in the Arctic, all lidar measurements showed total depolarization values for the Pinatubo stratospheric aerosol layer varying between 2% and 4%. If multiple scattering is negligible, the radiation backscattered by a polydispersion of spheres has the same polarization as the incident light. There is always some depolarization of a lidar return because of the anisotropy of the polarizability of the air molecules, but depolarization in the signal returned from aerosols indicates the presence of non-spherical particles. In this paper, we utilize scattering calculations for non-spherical particles to explore interpretations of lidar signals returned by Pinatubo aerosols. Taking into account several particle shapes and log-normal size distributions, calculations show that only slightly-to-moderate deformed spheres with equivalent-mean-radius less than 0.2 &mgr;m yield depolarization values in the range given by the lidar measurements, if such particles form a substantial fraction of the population. The implications of particle non-sphericity on the retrieval of the aerosol size distribution are discussed. ¿American Geophysical Union 1994