Coordinated observations with lidar and balloon-borne particle counters were used to characterize polar stratospheric clouds and to estimate a particle index of refraction. The index of refraction was estimated from comparisons of calculated and measured scattering ratios at a wavelength of 532 nm. The clouds, measured from McMurdo Station, Antarctica (78 ¿S), were observed above 11 km at temperatures below 198 K and were divided into three classes based on their scattering properties and particle size. Clouds with a low scattering ratio, high depolarization, and significant fraction of particles with radii of >2.0 μm had a mean index of refraction of 1.42¿0.04 and a mode of 1.43. Clouds with a moderate scattering ratio, low depolarization, and fewer particles of >2.0 μm, had a mean index of refraction of 1.39¿0.03 and a mode of 1.37. Ice clouds, apparent from measurements of high scattering ratio, high depolarization, and high concentrations of particles of >1.0 μm, had a mean index of refraction of 1.32¿0.02 and a mode of 1.31. Measurements in volcanic aerosol indicated a mean index of 1.43¿0.04. ¿ American Geophysical Union 1995