The molecular motions of tetramethylammonium bromide (TMA-Br) in the solid phase were investigated by means of the temperature dependence of the proton magnetic resonance line width and of the spin lattice relaxation time at several frequencies (6, 8, 16, 30, and 59 MHz). The results indicate the presence of two motions: (1) methyl reorientation about its threefold axis (T> 150 K) and (2) isotropic tumbling of the cation (T > 230 K). Activation energies and frequency factors of the two motions were evaluated. The double minima, observed in the temperature variation of T1, were attributed to the above motions. The T1 data for the various frequencies in the whole measured temperature region were analyzed using Woessner's treatment improved by the inclusion of intermethyl interactions.