The influences of substrate temperature, deposition rate and film thickness on the structure of erbium films deposited on molybdenum substrates of surface roughness Rq=151 nm are investigated by energy-dispersive x-ray diffraction. This shows that erbium polycrystalline films grow preferentially in the 〈001〉 direction. The intensity ratio of the Er(002) peak to Er(101) increases with film thickness, in particular above 300 nm thickness. The influence of direction of the incident evaporated beam at 8.5°to the normal is also investigated and it is shown that at low substrate temperature the film orientation is offset, but at higher temperatures (Ts≥575 K) the film orientation becomes normal to the substrate. Such controllable preferred orientation may be of value in the fabrication of diffracting components for x-ray instrumentation.