We present the results of a detailed study of the first and second-order Raman scattering in wurtzite GaN and AlN at room and liquid helium temperatures. A complete group-theory analysis of phonon symmetry and optical selection rules permitted us to assign the observed features in the second-order Raman spectra to combinations of phonons at the Γ, K, and M points of the Brillouin zone. The joint treatment of these results with lattice dynamical calculations based on phenomenological interatomic potential model allowed us to obtain the reliable data on phonon dispersion curves in bulk GaN and AlN.