The structure and crystallinity of plasticized poly(vinyl chloride) (PVC) has been examined using small-angle neutron scattering (SANS) and a deuterated plasticizer. The scattering curve, which shows a prominent peak at a Bragg spacing of ∼ 11 nm, has been interpreted using a two-phase model where the phases are assumed to be plasticized amorphous material and unplasticized, probably crystalline, material. The volume fraction of the PVC that was unplasticized was obtained from the SANS invariant. The value found, 0.29, was relatively insensitive to the assumed amorphous density and consistent with the dependance of the scattering peak height on the fraction of the plasticizer that was deuterated. © 1986.