The reflectivity of thin‐film multilayers near the critical angle for total reflection was measured with Cu‐Kα1 x radiation. The observed small‐angle interference patterns were compared with the results of the reflectivity computation for a model structure consisting of a number of stratified layers on a flat substrate. The model parameters, thicknesses and refractive indices of the layers, were optimized using the non‐linear simplex method. Discussed are results obtained for Langmuir‐Blodgett‐type Mn‐stearate multilayers, (Ga,Al)As superlattices and for near‐periodic multilayers of an amorphous W‐Re alloy and carbon.