In this work we present the theory of the scattering of light from an anisotropic semiinfinite medium. We show that the Brillouin scatterin can occour with two different mechanisms. The first one is related to the surface corrucation induced by the thermal phonons. The ripple effect is dominant in the scattering from metalli surfaces where the penetration depth of the light is very small. The second scattering mechanism is due to the modulation of the dielectric function of the whole medium induced by the phonons. It results particularly important for opaque semiconductors (elastooptic effect). In order to investigate the effects of the anisotropy of the medium we prent results for various faces of clean semiconductors.