An ellipsometric method for determining the optical constants and optic axis orientations of a biaxially stretched plastic film is described. This technique works hy making angularly resolved generalized anisotropic ellipsometric measurements in transmission and reflection and does not require special or multiple sample azimuthal orientations. The measured data is then subjected to a. model regression procedure which can account for the propagation of multiple beams through biaxially anisotropic layers. The results are consistent with Abbe refractometer measurements. The ellipsometric results near normal incidence also indicate that the in-plane optic axes are twisted through the layer.