Time-resolved small angle X-ray scattering has been used to study the electric field-induced motion of the smectic layers in an antiferroelectric liquid crystal on switching between the field-induced ferroelectric states. The intensity and position of the Bragg peak was recorded with 10 μs time resolution across a bipolar switching pulse of period 2ms. Reversible layer reorganization and motion were observed to occur within the first 500 μs of applying the switching field. The data show that the antiferroelectric liquid crystal switches from one ferroelectric state to the other with an increase in layer spacing of around 0.1 Å, a rotation of the layer normal of 0.5° and a reduction in the angular width of the diffraction peak by 1.7°. Subsequent relaxation of the layers occurs with the characteristic of a van der Pol oscillator. A model is presented that illustrates the form of the rapid and reversible layer motion. © 2006 Taylor & Francis.