In the last two decades, a large amount of experimental data has been collected about acoustic, electromagnetic, and subatomic particle emissions from solid media subjected to brittle fracture. This experimental evidence can be explained by considering the close relationship between the frequency of pressure waves generated during the fracture process and the size of the forming cracks. Based on the preceding observations, in the present chapter neutron emission measurements are applied for the first time in the early-stage fatigue diagnosis of metallic materials. The attention is focused onto the fatigue behavior of EN-AW6082 aluminum alloy specimens in the Very High Cycle Fatigue (VHCF) regime. In order to investigate the scale effects on both fatigue resistance and neutron emission, five different diameters in the middle cross-section of the specimens are selected between 3 and 30 mm. The VHCF tests are performed by means of an ultrasonic fatigue testing machine able to reach 1010 cycles in approximately one week. The experimental results show a decrement in the fatigue resistance by increasing the specimen size. In addition, considerable neutron emissions are revealed during the fatigue tests, which are correlated to micro- and nano-cracking in the samples. Furthermore, an increment in the neutron emission is found by increasing the specimen diameter in the middle cross-section. These results permit to consider the application of neutron emissions as a new and promising structural health monitoring technique for critical components subjected to fatigue damage initiation and accumulation.