A general relation is derived which describes the spatio-temporal behaviour of space charge in an ideal dielectric medium. (Diffusion effects are neglected.) This result is used to determine the behaviour of a parallel plate capacitor which contains space charges near its electrodes. Expressions are derived for the variation with time of the potential difference between the plates following the removal of an applied voltage and for the external current which flows when the plates are connected together. Symmetrical and asymmetrical charge distributions are considered.