Interionic interactions in a crystal of 4,5-diiodo-3-methyl-1-propylimidazolium hexafluorophosphate were investigated. This salt crystallizes in the monoclinic system, space group P2₁/c with cell parameters of a = 11.5373(6), b = 8.6305(5), c = 15.3770(8)Å, β = 107.1410(10)°, V = 1463.12(14)ų, and Z = 4. The crystal structure was solved by a direct method and refined by full-matrix least squares to a final R value of 0.0291 with I > 2σ(I). C-I…F halogen bonding, C-H…F hydrogen bonding and C…F electrostatic interactions were found in this crystal.