An accurate determination of the field-dependent spin relaxation rates of Br-81 by NMR provides, through the motional correlation time, the lateral surface diffusion coefficient of the Br- ions that are electrostatically confined to the vicinity of the oppositely charged surface of C(16)TABr micelles. We find that the Br- counterions diffuse about 1 order of magnitude faster than the C(16)TA(+) molecules. The obtained diffusion coefficient is about 10(-9) m(2)/s, roughly half the bulk diffusion coefficient of Br-. The residual quadrupole coupling constant is small, around 1 MHz, indicating a high symmetry for the Br- environment on the greater than or equal to 100 ps time scale.