The pore structure of series of porous styrene–divinylbenzene resins has been monitored both in the non-swollen state and when swollen with a range of solvents of varying Hildebrand solubility parameter using small-angle neutron scattering. It has been shown that the Porod scattering invariants increase as swelling increases, indicating an increase in the interfacial scattering surface area. For the sample prepared with a relatively small amounts of porogen during polymerization, the scattering curves of the acetic acid and toluene swollen samples each consist of two linear regions up to ca. 45 Å is size, corresponding firstly to scattering from swollen, highly crosslinked regions and secondly to mass fractal aggregates of these regions. Samples produced with higher amounts of porogen have a surface fractal structure in the swollen state. Porosity that is closed to the external surface in dry samples is accessible to swelling solvents.