The microphase behavior of lightly sulfonated polystyrene solutions in Decalin was investigated using dynamic light scattering. The nature of the aggregates formed in these solutions by the association of the sulfonic acid groups was dependent on the temperature and concentration. At high concentrations, aggregates persisted to temperatures far above the cloud point temperatures. At low concentrations, the aggregates were absent except near the cloud point temperatures. The aggregation increased as one approached the cloud point, thereby indicating that the extensive aggregation provides the driving force for phase separation in these solutions at temperatures higher than that for the precursor polystyrene solutions.