The electronic structure of the flavylium cation (1) and those of some of its hydroxylated derivatives were studied by semiempirical and ab initio molecular orbital methods. This ion presents a small resonance in the pyrylium group (C-ring), which is not conjugated to the phenyl group (B-ring). The planarity of the molecule is due to a hydrogen bond between the oxygen atom in C-ring and some hydrogen atoms in B-ring. There is also a repulsive interaction between hydrogen atoms of these rings. The theoretical locations of the sites of nucleophilic and electrophilic attack corresponds to those experimentally observed. Monohydroxylation does not cause important alterations in the electronic structure of the cation (1) except for the substitution on C(4 ), which causes the appearance of resonance between B- and C-rings.