This paper investigates the flow of a particle filled polystyrene melt through a constriction zone using a combination of experimental techniques and computer simulation. A special blend, containing cross-linked polystyrene beads mixed into a polydispersed polystyrene matrix, was produced for this study. This closely refractive index matched blend allowed visualization of the flow birefringence up to an equivalent particle loading of around 15 vol¿%. Flow birefringence through a 10:1.4 contraction, measured using a multi-pass rheometer (MPR), was compared with that predicted from finite element simulations, in a similar way to that already published for unfilled polymer melts [ Collis et al., J. Rheol. 49(2), 501–522 (2005) ]. Numerical predictions were obtained using the finite element solver "EUFLOW" and ranked against the experimental processing data from the MPR. An extensive study of the rheology of the particle filled polystyrene blend was conducted which provided the input to the simulations. The addition of the particles was seen to enhance the shear thinning of the melt, while debonding between the particles and the polystyrene melt during extension testing had the effect of reducing strain hardening. EUFLOW was used to evaluate how these two important aspects could affect the flow birefringence of the filled polystyrene melt.