Iodic acid crystallises from acidic solution as orthorhombic α- in space group P222. The structure consists of pyramidal molecules linked by hydrogen bonding and intermolecular iodine-oxygen interactions. The I=O bond lengths are 1.81 Å while the I–OH distance is 1.89 Å. Several other polymorphs have been reported, including an orthorhombic γ form in space group Pbca and an orthorhombic δ form in space group P222. All of the polymorphs contain pyramidal molecules, hydrogen bonding and I···O interactions, but differ in packing arrangement.