The crystal structure of kinetin dihydrogenphosphate has been determined at 115 and 293 K. Kinetin dihydrogenphosphate undergoes a polymorphic phase transition at 291.1 K. In both phases the crystal belongs to the triclinic system with the symmetry described by the space group P\bar 1. In the low-temperature phase, the unit cell is doubled along the a axis. There is a dynamic equilibrium between different tautomeric forms of the adenine residue, determined by the distribution of H atoms within the network of hydrogen bonds.