The tautomeric structures of free-base porphyrin-type compounds reflect a fascinating interplay of hydrogen bonding, aromaticity, steric effects, and solvation. Furthermore, the tautomerism is critical to applications of the compounds as components of emerging molecular-electronic and memory-storage devices. A great deal of study, accordingly, has been devoted to the study of tautomerism in porphyrins, N-confused porphyrins, porphycenes, hydroporphyrins, phthalocyanines, expanded porphyrins, and corroles. Even when presenting the very first synthesis of a corrole, Johnson and Kay noted that it forms a stable anion. Subsequently, several researchers noted the deprotonation of corroles by mild bases and even simply by polar solvents such as DMF, while Gross et al. determined the apparent acidity constant of an amphiphilic corrole. Corrole anions were found to exhibit more intense Q bands relative to the neutral, free-base forms. Kadish found that corrole anions (H2Cor -) undergo electrooxidation and electroreduction to yield neutral radicals (H2Cor • ) and anion-diradicals (H2Cor •2-), respectively. A key aspect of free-base corrole anions, however, has remained unclear: their structure (Scheme 1). While there is extensive evidence that free-base corroles exist as a pair of essentially equienergetic tautomers, key questions remain about the tautomeric structure of the anions. Is the trans tautomer, the one experimentally observed in this study, the only low-energy tautomer? Do the two equienergetic trans tautomers (AC and BD in Scheme 1) readily interconvert? If so, are cis tautomers (one or more among AB, CD, BC, and AD) involved as intermediates? Might the cis tautomers prove observable or even isolable? Herein we present the X-ray structure of free-base tris(p-cyanophenyl)corrole anion and an extensive set of DFT calculations that shed light on the these questions.