Abstract The crystal structure and the magnetic ordering of the novel orthorhombic compound ErGe 2−x has been studied by neutron powder diffraction and magnetic measurements. The crystal structure belongs to the DyGe 1.85-type (space group Cmc2 1)·ErGe 2−x ( x = 0.17 (2)) orders antiferromagnetically below T N = 6 K and displays a metamagnetic behaviour. The magnetic cell has the same size as the chemical unit cell ( q = 0 ). The magnetic space group is Cmc2 1 (Sh 36 173). At T = 1.5 K the magnetic moments of the two erbium sites have the same ordered magnetic moment values of 7.63 (6) μ B/Er and are antiferromagnetically coupled leading to an uniaxial structure along the a direction.