The first-order isotopic difference method of neutron diffraction was applied to the iron ions of an acidic 1 molal solution of iron chloride in heavy water. Results were obtained for the Fe²⁺ hydration; these show that this ion is hexahydrated with nearest neighbour Fe. . .O and Fe. . .D distances of 2.12(2)AA and 2.75(5)AA, respectively. There is also evidence of a weak second hydration shell.