The paper deals with the influence of one-dimensional diffusion of small interstitial clusters produced in collision cascades on the swelling of irradiated structural materials. It is demonstrated that the resulting swelling modification is very sensitive to microstructural parameters of irradiated materials. Qualitative trends of swelling modification in well annealed materials correlate with experimental observations; however for cold-worked materials the model predicts noticeable decrease in swelling rate by one-dimensionally diffusing clusters, which is in contrast with the observed material behaviour.