  We report strong variability in the circular and linear polarization of the
intraday variable source PKS 1519-273. The circular polarization varies on a
timescale of hours to days at frequencies between 1.4 and 8.6 GHz, and is
strongly correlated with variations in the total intensity at 4.8 and 8.6 GHz.
We argue that the variability is due to interstellar scintillation of a highly
compact (15-35 \mu as) component of the source with -3.8\pm 0.4% circular
polarization at 4.8 GHz. We find that no simple model for the circular
polarization can account for both the high magnitude and the frequency
dependence in PKS 1519-273 at centimeter wavelengths.
