Relativistic density functional calculations are used to examine the spectroscopic parameters of [Hg(cyclam)]³⁺ (cyclam=1,4,8,11‐tetraazacyclotetradecane), which is thought to contain Hg³⁺, and to analyze its electronic structure. Although the computed EPR parameters and excitation energies are consistent with the experimental data, a detailed analysis of the electronic structure contradicts the assignment as an Hgᴵᴵᴵ complex.