We describe a method for generating glass structures of polymers containing large monomer units for use in molecular simulations. This method is an extension of the technique proposed by Rigby and Roe (Rigby, D.; Roe, R. J. Chem. Phys. 1987, 87, 7285) for short-chain alkanes and involves a “polymerization” of randomly placed monomers in the simulation box. An optimum polymerization sequence is found by the technique of simulated annealing, and a well relaxed glass structure is generated from this sequence by a combination of molecular mechanics and molecular dynamics simulations. We have used the technique to prepare 10 glass structure of polystyrene, for which we have calculated average structural properties. The amorphous nature of these structures is demonstrated by the absence of long-range orientational correlations for the chain backbone. The phenyl rings also show a preference to pack at a distance of 5–6 Å and to align at right angles to one another.