The dimensional changes occurring in metals under fast-neutron irradiation and external loads have been analyzed in terms of dislocation climb and glide, dislocation loop formation, and diffusional growth of voids. The strains produced by these mechanisms were derived. Although these strains can be divided into swelling strains and creep strains, the irradiation creep strains may be related to the swelling strains. Strains produced by the climb of dislocations contribute mainly to swelling, but not to irradiation creep. However, if the glide of dislocations is controlled by the climb motion, the resulting irradiation creep rate is directly proportional to the swelling rate. Preferential loop nucleation induced by external stresses gives rise to an irradiation creep correlation which is in agreement with the experimental data.