Lattice dynamics (LD) and molecular dynamics (MD) calculations have been used to investigate phonons propagating in monolayers, bilayers and trilayers of rare gases physisorbed on the Ag(111) surface. Adatom–surface potentials for the monolayers are represented by a Morse function whose well depth and curvature are parametrized to reproduce the latent heat of condensation and the frequency of the dispersionless phonon branch with atomic displacements perpendicular to the surface. In the bilayers and trilayers the second and third overlayers are assumed to interact with the surface via the known van der Waals terms. Realistic potentials are used to represent the interactions between the adatoms. If the interlayer separations are optimized with due allowance for thermal dilation effects the LD results are in agreement both with the MD calculations and with the available experimental data for the bilayers and trilayers. The sensitivity of the calculations to variations in the parameters of the model potential has been investigated.