The Lorentz-Lorenz relation is used to estimate the refractive index of aqueous H2SO4/HNO3 solutions (5--70 wt%) for wavelengths from the near-ultraviolet to the near-infrared (0.35--2 &mgr;m) and for temperatures from 370 K to stratospheric temperatures (185 K). The molecular refractivities of the involved species are based on data of the binary solutions at room temperature. For the extrapolation to low temperatures, a careful estimate of the density of the ternary solutions has been performed. The accuracy of the model predictions is estimated to be better than 2%. ¿ American Geophysical Union 1996