The influence of the surface condition and elevated temperature on the fatigue properties of high pressure die cast magnesium alloy AS21X was investigated. Separately cast specimens were tested under tensile cyclic loading, at room temperature and 150 degrees C. With the as-cast surface layer intact, no significant temperature influence on fatigue life was found for large stress amplitudes, whereas the fatigue strength at 107 cycles was found to drop from 50 MPa at 20 degrees C to 40 MPa at 150 degrees C. Fracture surface analysis revealed that the predominant fatigue cracks originated from pre-existing surface defects.