The ternary iridium borides REIr 2B 2 containing the light rare earth metals RE ≡ Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy were prepared and investigated by means of X-ray methods. LaIr 2B 2, SmIr 2B 2 and GdIr 2B 2 are high temperature phases. All the compounds crystallize in the orthorhombic space group Fddd with 8 formula units in the unit cell. The lattice constants for LaIr 2B 2 are a = 10.643(1) A ̊ ; b = 9.420(1) A ̊ ; c = 6.065(1) A ̊ (for the other compounds see Table 1). Structure determination using single crystals of CeIr 2B 2, EuIr 2B 2, GdIr 2B 2 and YIr 2B 2 showed that they had the CaRh 2B 2 structure. Judging from powder photographs the other compounds are similar. A plot of the unit cell volumes vs. the lanthanide atomic number shows that europium is divalent and cerium is trivalent in these compounds.