The method of molecular dynamics has been used to study the behaviour of a polymer chain made up of rigid interacting links with practically free internal rotation. A single slightly deformed crosslink, whose length is equal to the length of a link, is introduced into the chain. A condensed polymeric system at high temperature is discussed. It is shown that the translational and rotational mobility of the crosslink are appreciably impeded. The impeding effect of the crosslink spreads to a small number of adjacent chain elements (one link for the orientational mobility and 4–8 links for the translational mobility). The results of a numerical experimental are compared with an analytical calculation for a viscoelastic model of sub-chains with a crosslink and with experimental data obtained using polarization luminescence, the crosslink being labelled. The ways in which certain dynamic properties of crosslinked systems depend on the mole fraction of crosslinks have been calculated.