A theoretical analysis is presented for the development of a liquid film at the walls of vertically placed centrifugal separators. The liquid film arises at the walls of these separators due to the action of the centrifugal force on the entrained liquid phases. The analysis applies to situations for which the liquid load is small, i.e. the film thickness is much smaller than the height of the channel. This implies that the film can be regarded as a laminar boundary-layer type flow with negligible inertia effects. Solutions are presented for situations in which the liquid droplets flow co-currently and counter-currently with the gas flow.