Brillouin scattering is used to study the elastic behavior of oriented poly(ethylene terephthalate) films. The elastic constantsC11,C13,C33, andC44are determined by measurements of the quasilongitudinal and quasitransverse hypersonic velocities at different angles in the film. The total orientational parameter is calculated for the three draw ratios from the Brillouin hypersonic velocities and are found to be similar to the orientational parameter in the amorphous phase obtained with a different technique.