The present work demonstrates the first application of Brillouin light scattering to probe elastic excitations in highly anisotropic polymer thin films. Both the in-plane and out-of-plane longitudinal and shear moduli of poly(biphenyl dianhydride-p-phenylenediamine) (BPDA-PDA) polyimide were accessed by utilizing the transmission and reflection scattering geometries [Macromolecules 2007, 40, 7283; 2009, 42, 7164]. A series of thin BPDA-PDA polyimide coatings on transparent substrates with thickness in the range of 0.1-20 mu m were explored, and no noticeable trend in elastic properties and mechanical anisotropy with thickness has been found, in conformity with earlier results. The earlier studies were restricted to thick films (> 1.5 mu m) and to the in-plane moduli.