A continuum description of liquid helium II is proposed. Contrariwise to the twofluid model, it is supposed that helium II behaves like a single fluid with one internal degree of freedom. The analysis is based on the classical theory of irreversible processes. Despite its simplicity, the theory provides a satisfactory explanation of some of the oddly effects observed in He II. First and second sound velocities are calculated as well as their attenuation. The relations with Atkin and Fox’s single fluid model and Landau's two-fluid description are also examined. © Copyright by Walter de Gruyter & Co.