Tamimi, N., Tsvankin, I. and Davis, T.L., 2015. Estimation of VTI parameters using slowness-polarization inversion of P- and SV-waves. Journal of Seismic Exploration, 24: 455-474. Ignoring anisotropy may cause serious distortions in the results of seismic data processing and interpretation. Although P-wave data provide valuable information for estimating anisotropy parameters, important additional constraints can be obtained from shear waves. Here, we present an extension of the slowness-polarization method for VSP data, in which we combine the vertical slownesses and polarization angles of P- and SV-waves. The algorithm is developed for VTI (transversely isotropic with a vertical symmetry axis) media, but it can be generalized for azimuthally anisotropic models. The weak-anisotropy approximation shows that adding SV-wave data generally stabilizes slowness-polarization inversion. In particular, SV-waves improve not only estimation of the anellipticity parameter 7 but also help constrain the coefficient 6, if propagation angles around 45° are available. The proposed technique is applied to a synthetic VSP data set generated using a finite-difference code. This test confirms that including SV-waves yields better inversion results than those obtained solely from P-wave data.