The dynamics of micellized quaternary ammonium surfactants has been investigated by means of the frequency dependence of the 13C longitudinal relaxation rates. Trimethyl-, triethyl-, and tributyldodecylammonium bromides were used to systematically vary the bulk of the polar head and examine its influence on the internal and overall motions of the surfactants. The relaxation data were analyzed by means of the two-step model and of a rotational jump model relevant to the trans-gauche isomerizations about the bonds. In the case of the trimethyldodecyl--ammonium bromide an excellent agreement is obtained by the two-step model as the vicinity of the nitrogen is well above the values expected for methylene groups. The jump model shows that this behavior results from a slowing of the internal motions beyond the domain of validity of the two-step model.