The formation of mixed micelles composed of dodecyltrimethylammonium bromide (C12TAB) and a hexamethylated p-sulfonatocalixarene (SC6HM) was studied by several techniques. It was found that above the critical aggregation concentration the concentrations of free and micellized surfactant are strongly related to that of SC6HM. When there is free SC6HM in solution, the addition of C12TAB mainly results in an increase in the concentration of micellized surfactant, but when all SC6HM has been aggregated, the addition of C12TAB results in a substantial increase in the concentration of free surfactant in solution. When the concentration of free surfactant is equal to the critical micelle concentration of the pure system, a second independent aggregation process is observed. This aggregation behavior has many features that are similar to those of more complex systems that involve surfactants in the presence of oppositely charged polyelectrolytes. In this way, calixarenes can serve as simple models to mimic polyelectrolytes and to gain insight into the complex behavior displayed by these macromolecules.