A possible structural model for the mesomorphic form of syndiotactic poly(p-methylstyrene) is discussed. The structural analysis is performed through the comparison between the experimental X-ray diffraction intensities and the calculated intensities for model structures constituted by ordered and disordered aggregates of chains. This analysis provides support for the hypothesis that the mesomorphic form of sPPMS may be described in terms of small aggregates of trans-planar chains having a packing mode very close to that one of form III, in which disorder in the relative arrangement of neighbouring chains is present to some extent.