Results of ab initio self-consistent-field and density functional theory calculations of the gas-phase structure, acidity (free energy of deprotonation, Delta G(0)) and aromaticity of 1,2-dithio-3,4-diselenosquaric acid (3,4-diselenyl-3-cyclobutene-1,2-dithlone, H2C4S2Se2) an reported. The optimised geometrical parameters result in an equalization of the bond lengths compared with the reference compounds cyclobutandithione and cyclobutenediselenol. The computed aromatic stabilization energy and diamagnetic susceptibility exaltation (Lambda) are negative, indicating that 1,2-dithio-3,4-diselenosquaric acid is aromatic. Thus, 1,2-dithio-3,4-diselenosquaric acid fulfils the geometrical energetic and magnetic criteria of aromaticity.