Vesicles form spontaneously in a variety of aqueous mixtures of oppositely charged surfactants. Here we report the morphological transition from spherical micelles to vesicles observed in mixtures of dodecyltrimethylammonium chloride (DTAC) and sodium dodecylbenzenesulfonate (SDBS) as probed by the complementary techniques of quasielastic light scattering (QLS), NMR self-diffusion and relaxation measurements, and time-resolved fluorescence quenching (TRFQ) experiments. In these mixtures, there is limited growth of the micelles with changes in composition, and vesicles abruptly begin to form at a characteristic mixing ratio of the two surfactants. As the composition moves further into the vesicle region, the quantity of micelles decreases in proportion to the number of vesicles that form. Thus, in mixtures of DTAC and SDBS, the transition from micelles to vesicles is continuous. This is in contrast to the first-order phase transition exhibited by other aqueous mixtures of oppositely charged surfactants, in which micelles first grow into extended threadlike micelles and samples intermediate to the micellar and vesicle phases separate into two macroscopic phases.