A method is provided for determining the viscosity of thin films which exhibit a viscous behavior at a measurement temperature, notably for polymer resins above their glass transition temperature. A thin layer of material is formed on a substrate, a known geometrical pattern is impressed in the thin layer by molding or etching, the thin layer being in the solid state at the end of the impression step. The initial topography of the impressed pattern is measured over the entire length of the pattern along a determined direction, the film is baked at the measurement temperature Tm for a determined creep time tflu, and the resulting topography of the crept pattern is measured. Mathematical processing of the topography measurements is carried out in order to deduce a value of viscosity at the measurement temperature therefrom. The impressed pattern at the start is aperiodic.