The dielectric relaxation is studied of linear and cross-linked polyurethane based on linear and three-armed star poly(propylene oxide), also called poly(propylene glycol). The dielectric relaxation of polyurethane melts and gels is indistinguishable if the density of urethane links is the same. The introduction of urethane links slows down the segmental relaxation of a number of segments adjacent to the links. The influence is much stronger on the dielectric relaxation than on the relaxation of the shear modulus. The relaxation of the end-to-end vector of the PPO precursors is not much influenced by end-linking at least as long as they are not strongly entangled.