The electrochemical oxidation of 1,4-bis(methylseleno)benzene (la) was studied in acetonitrile by conventional and microelectrode techniques. Using untreated acetonitrile (0.02% nominal water content)/0.10 M NaClO4, cyclic voltammetry showed two irreversible bielectronic oxidation signals, corresponding to the consecutive oxidation of both selenium atoms into their selenoxides, as evidenced by controlled potential coulometry and electrolysis. In superdry acetonitrile/0.10 M tetra-n-butylammonium hexafluorophosphate (TBAPF(6)), the reversible oxidation of la into its radical cation was observed. Semiempirical computations by the parametric method 3 (PM3) evidenced that the unusual stability of this species compared to radical cations of both alkylaryl-and diarylselenides is due to the equal distribution of the positive charge on both selenium atoms. Investigation of this first electron transfer and the following process by cyclic voltammetry at various scan rates, temperatures, and concentrations, indicated that the radical cation of la dimerizes reversibly into a dication, which is according to PM3 computations energetically favored by 368 kJ mol(-1). The dimeric dication can be considered to be formed by two intermolecular two-center three-electron Se-Se bonds.