Density functional theory (DFT) and polarizable continuum solvation model (PCM) calculations have been applied to the study of the acid/base and prototropic equilibria of anthocyanidins. The results indicate that, excluding pelargonidin, the most favored neutral tautomers in solution are deprotonated at C4'. With the same exception, deprotonations at C5 and C4' characterize the most stable anionic tautomers in solution. The equilibrium population of tautomers is mainly modified along the series by the substitution pattern on the B-ring. Electron densities, analyzed within the formalism of the quantum theory of atoms in molecules (QTAIM), indicate that the electron distribution of cations, neutral forms, and anions is not well described by the Lewis structures usually employed to represent them.