On the basis of the electrochemical results obtained for thin films of 7,7,8,8-tetracyanoquinodimethane (TCNQ) on a glassy carbon electrode, the reduction and oxidation of the [TCNQ](0/-) couple in KCl aqueous media occurs via a mechanism involving layer-by-layer nucleation and growth. In situ recorded UV-visible spectroelectrochemical data allow two different crystal structures for the oxidized form of TCNQ to be discriminated.