The role that dislocations are likely to play in chain-folded polymer crystals is examined, particularly with regard to their influence on plastic deformation. It is assumed that primary bonds cannot be broken in backbone molecular chains; and this restriction, to-gether with further restrictions brought about by chain folding, limits substantially the number of permissible dislocations and glide processes. It is shown that deformations of appreciable magnitude in chain-folded polymer crystals almost certainly cannot be attributed solely to dislocation mechanisms. Crystals of the n-alkanes and "extended chain" polymer crystals are also discussed briefly.