The aggregation behavior of omega- and alpha,omega-metal sulfonato polystyrene in toluene has been investigated by static and dynamic light scattering. Monofunctional chains reversibly associate into small reverse micelles. Lithium-based ionic aggregates contain an average of 12 ion pairs, which corresponds to a preferential structure for the ionic cores. When the molecular weight of the chains is increased, polymer-solvent interactions progressively distort the ionic aggregates, and above a critical molecular weight, estimated to be 50000 in toluene, the multiplets collapse into smaller aggregates of an average of 3 ion pairs. Traces of polar solvents do not strongly affect the aggregation number, but do weaken the dipole-dipole interactions. Structure of the ionic cores strongly depends on the nature of the ion pairs, which suggests that this structural feature is a key parameter in the control of the structure-property relationships in ionomers. The aggregation behavior of the difunctional chains is complex, due to the occurrence of a closed association mechanism for the individual multiplets and an open association of reverse micelles into larger aggregates.